Three-dimensional memory device containing bump stack structures and method of deformation measurement thereof

ABSTRACT

A three-dimensional memory device includes an alternating stack of insulating layers and electrically conductive layers, pillar structures vertically extending through the alternating stack, bump stack structures including a base bump portion located underneath the alternating stack and a respective subset of the bump portions located in the alternating stack that overlie the base bump portion, and protrusion structures located over the alternating stack and laterally spaced from the bump stack structures. Each of the insulating layers and the electrically conductive layers include a planar portion located between a planar top surface and a planar bottom surface and the bump portions that are adjoined to the planar portion at a respective periphery and having a respective raised top surface that is vertically raised from the planar top surface and a respective raised bottom surface that is raised from the planar bottom surface.

FIELD

The present disclosure relates generally to the field of semiconductordevices, and particularly to a method of using bump stack structures formeasurement of deformation during manufacture of a three-dimensionalmemory device and the three-dimensional memory device formed by themethod.

BACKGROUND

A three-dimensional memory device including three-dimensional verticalNAND strings having one bit per cell are disclosed in an article by T.Endoh et al., titled “Novel Ultra High Density Memory With AStacked-Surrounding Gate Transistor (S-SGT) Structured Cell”, IEDM Proc.(2001) 33-36.

SUMMARY

According to an embodiment of the present disclosure, athree-dimensional memory device includes an alternating stack ofinsulating layers and electrically conductive layers, pillar structuresvertically extending through the alternating stack, bump stackstructures including a base bump portion located underneath thealternating stack and a respective subset of the bump portions locatedin the alternating stack that overlie the base bump portion, andprotrusion structures located over the alternating stack and laterallyspaced from the bump stack structures. Each of the insulating layers andthe electrically conductive layers include a planar portion locatedbetween a planar top surface and a planar bottom surface and the bumpportions that are adjoined to the planar portion at a respectiveperiphery and having a respective raised top surface that is verticallyraised from the planar top surface and a respective raised bottomsurface that is raised from the planar bottom surface.

According to another embodiment of the present disclosure, a method offorming a semiconductor structure comprises forming base bump portionsover a substrate, forming an alternating stack of insulating layers andspacer material layers, wherein the spacer material layers are formedas, or are subsequently replaced with, electrically conductive layers,wherein each layer within the alternating stack comprises a planarportion vertically extending between a planar top surface and a planarbottom surface and bump portions that overlie a respective one of thebase bump portions to form bump stack structures comprising a respectiveone of the base bump portions and a respective subset of the bumpportions of the alternating stack are formed, forming protrusionstructures located over the alternating stack and laterally spaced fromthe bump stack structures, and forming pillar structures through thealternating stack, wherein each of the pillar structures comprises amemory film and a vertical semiconductor channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a plan view of a unit die area in an exemplary structure thatincludes a substrate and a plurality of semiconductor dies according toan embodiment of the present disclosure.

FIG. 1B is a vertical cross-sectional view of the exemplary structurealong the vertical cross-sectional plane B-B′ of FIG. 1A after formationof semiconductor devices, lower level dielectric layers, lower metalinterconnect structures, and in-process source level material layers ona semiconductor substrate according to an embodiment of the presentdisclosure.

FIG. 1C is a magnified view of the in-process source level materiallayers of FIG. 1B.

FIG. 1D is a top-down view of a region D of the exemplary structure ofFIG. 1A. The hinged vertical cross-sectional plane B-B′ is the plane ofthe vertical cross-sectional view of FIG. 1B.

FIG. 1E is a perspective view of a source-select-level semiconductorlayer in the exemplary structure of FIGS. 1A-1D.

FIG. 1F is a vertical cross-sectional view of the source-select-levelsemiconductor layer along the vertical plane F-F′ of FIG. 1D.

FIG. 2 is a vertical cross-sectional view of the exemplary structureafter formation of a first-tier alternating stack of first insultinglayers and first spacer material layers according to an embodiment ofthe present disclosure.

FIG. 3A is a vertical cross-sectional view of the exemplary structureafter deposition of a first patterning film and a first etch mask layeraccording to an embodiment of the present disclosure.

FIG. 3B is a perspective view of a portion of the exemplary structure ofFIG. 3A.

FIG. 3C is a vertical cross-sectional view along the plane C-C′ of theexemplary structure of FIG. 3B.

FIG. 4A is a vertical cross-sectional view of the exemplary structureafter deposition of a first bottom antireflective coating (BARC) layerand a photoresist layer according to an embodiment of the presentdisclosure.

FIG. 4B is a perspective view of a portion of the exemplary structure ofFIG. 4A.

FIG. 4C is a vertical cross-sectional view along the plane C-C′ of theexemplary structure of FIG. 4B.

FIG. 5A is a vertical cross-sectional view of the exemplary structureafter formation of first-tier memory openings and first-tier supportopenings according to an embodiment of the present disclosure.

FIG. 5B is a horizontal cross-sectional view of the exemplary structureof FIG. 5A. The hinged vertical plane A-A′ corresponds to the plane ofthe vertical cross-sectional view of FIG. 5A.

FIG. 6 is a vertical cross-sectional view of the exemplary structureafter formation of various sacrificial fill structures according to anembodiment of the present disclosure.

FIG. 7A is a vertical cross-sectional view of the exemplary structureafter formation of a second-tier alternating stack of second insulatinglayers and second spacer material layers, second stepped surfaces, and asecond retro-stepped dielectric material portion according to anembodiment of the present disclosure.

FIG. 7B is a perspective view of a portion of the exemplary structure ofFIG. 7A.

FIG. 7C is a vertical cross-sectional view along the plane C-C′ of theexemplary structure of FIG. 7B.

FIG. 8A is a vertical cross-sectional view of the exemplary structureafter deposition of a second patterning film and a second etch masklayer according to an embodiment of the present disclosure.

FIG. 8B is a perspective view of a portion of the exemplary structure ofFIG. 8A.

FIG. 8C is a vertical cross-sectional view along the plane C-C′ of theexemplary structure of FIG. 8B.

FIG. 9A is a vertical cross-sectional view of the exemplary structureafter formation of second-tier memory openings and second-tier supportopenings according to an embodiment of the present disclosure.

FIG. 9B is a horizontal cross-sectional view of the exemplary structurealong the horizontal plane B-B′ of FIG. 9A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 9A.

FIG. 10 is a vertical cross-sectional view of the exemplary structureafter formation of inter-tier memory openings and inter-tier supportopenings according to an embodiment of the present disclosure.

FIGS. 11A-11D illustrate sequential vertical cross-sectional views of amemory opening during formation of a memory pillar structure accordingto an embodiment of the present disclosure.

FIG. 12 is a vertical cross-sectional view of the exemplary structureafter formation of memory pillar structures and support pillarstructures according to an embodiment of the present disclosure.

FIG. 13A is a vertical cross-sectional view of the exemplary structureafter formation of a first contact-level dielectric layer and backsidetrenches according to an embodiment of the present disclosure.

FIG. 13B is a horizontal cross-sectional view of the exemplary structurealong the horizontal plane B-B′ of FIG. 13A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 13A.

FIG. 14 is a vertical cross-sectional view of the exemplary structureafter formation of backside trench spacers according to an embodiment ofthe present disclosure.

FIGS. 15A-15E illustrate sequential vertical cross-sectional views ofmemory pillar structures and a backside trench during formation ofsource-level material layers according to an embodiment of the presentdisclosure.

FIG. 16 is a vertical cross-sectional view of the exemplary structureafter formation of source-level material layers according to anembodiment of the present disclosure.

FIG. 17 is a vertical cross-sectional view of the exemplary structureafter formation of backside recesses according to an embodiment of thepresent disclosure.

FIG. 18A is a vertical cross-sectional view of the exemplary structureafter formation of electrically conductive layers according to anembodiment of the present disclosure.

FIG. 18B is a horizontal cross-sectional view of the exemplary structurealong the horizontal plane B-B′ of FIG. 18A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 18A.

FIG. 19A is a vertical cross-sectional view of the exemplary structureafter formation of backside trench fill structures in the backsidetrenches according to an embodiment of the present disclosure.

FIG. 19B is a horizontal cross-sectional view of the exemplary structurealong the horizontal plane B-B′ of FIG. 19A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 19A.

FIG. 19C is a vertical cross-sectional view of the exemplary structurealong the vertical plane C-C′ of FIG. 19B.

FIG. 20A is a vertical cross-sectional view of the exemplary structureafter formation of a second contact-level dielectric layer and variouscontact via structures according to an embodiment of the presentdisclosure.

FIG. 20B is a horizontal cross-sectional view of the exemplary structurealong the vertical plane B-B′ of FIG. 20A. The hinged vertical planeA-A′ corresponds to the plane of the vertical cross-sectional view ofFIG. 20A.

FIG. 21 is a vertical cross-sectional view of the exemplary structureafter formation of through-memory-level via structures and upper metalline structures according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

As discussed above, the embodiments of the present disclosure aredirected to a method of using bump stack structures for measurement ofdeformation during manufacture of a three-dimensional memory device andthe three-dimensional memory device formed by the method, the variousaspects of which are described herein in detail. The bump stackstructures may be used for intra-die overlay monitoring duringfabrication of the three-dimensional memory device. The embodiments ofthe present disclosure may be used to form various semiconductor devicessuch as three-dimensional monolithic memory array devices comprising aplurality of NAND memory strings. The drawings are not drawn to scale.

The drawings are not drawn to scale. Multiple instances of an elementmay be duplicated where a single instance of the element is illustrated,unless absence of duplication of elements is expressly described orclearly indicated otherwise. Ordinals such as “first,” “second,” and“third” are employed merely to identify similar elements, and differentordinals may be employed across the specification and the claims of theinstant disclosure. The term “at least one” element refers to allpossibilities including the possibility of a single element and thepossibility of multiple elements.

The same reference numerals refer to the same element or similarelement. Unless otherwise indicated, elements having the same referencenumerals are presumed to have the same composition and the samefunction. Unless otherwise indicated, a “contact” between elementsrefers to a direct contact between elements that provides an edge or asurface shared by the elements. If two or more elements are not indirect contact with each other or among one another, the two elementsare “disjoined from” each other or “disjoined among” one another. Asused herein, a first element located “on” a second element can belocated on the exterior side of a surface of the second element or onthe interior side of the second element. As used herein, a first elementis located “directly on” a second element if there exist a physicalcontact between a surface of the first element and a surface of thesecond element.

As used herein, a first element is “electrically connected to” a secondelement if there exists a conductive path consisting of at least oneconductive material between the first element and the second element. Asused herein, a “prototype” structure or an “in-process” structure refersto a transient structure that is subsequently modified in the shape orcomposition of at least one component therein.

As used herein, a “layer” refers to a material portion including aregion having a thickness. A layer may extend over the entirety of anunderlying or overlying structure, or may have an extent less than theextent of an underlying or overlying structure. Further, a layer may bea region of a homogeneous or inhomogeneous continuous structure that hasa thickness less than the thickness of the continuous structure. Forexample, a layer may be located between any pair of horizontal planesbetween, or at, a top surface and a bottom surface of the continuousstructure. A layer may extend horizontally, vertically, and/or along atapered surface. A substrate may be a layer, may include one or morelayers therein, or may have one or more layer thereupon, thereabove,and/or therebelow.

As used herein, a first surface and a second surface are “verticallycoincident” with each other if the second surface overlies or underliesthe first surface and there exists a vertical plane or a substantiallyvertical plane that includes the first surface and the second surface. Asubstantially vertical plane is a plane that extends straight along adirection that deviates from a vertical direction by an angle less than5 degrees. A vertical plane or a substantially vertical plane isstraight along a vertical direction or a substantially verticaldirection, and may, or may not, include a curvature along a directionthat is perpendicular to the vertical direction or the substantiallyvertical direction.

As used herein, a “memory level” or a “memory array level” refers to thelevel corresponding to a general region between a first horizontal plane(i.e., a plane parallel to the top surface of the substrate) includingtopmost surfaces of an array of memory elements and a second horizontalplane including bottommost surfaces of the array of memory elements. Asused herein, a “through-stack” element refers to an element thatvertically extends through a memory level.

As used herein, a “semiconducting material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0×10⁵ S/m.As used herein, a “semiconductor material” refers to a material havingelectrical conductivity in the range from 1.0×10⁻⁵ S/m to 1.0 S/m in theabsence of electrical dopants therein, and is capable of producing adoped material having electrical conductivity in a range from 1.0 S/m to1.0×10⁷ S/m upon suitable doping with an electrical dopant. As usedherein, an “electrical dopant” refers to a p-type dopant that adds ahole to a valence band within a band structure, or an n-type dopant thatadds an electron to a conduction band within a band structure. As usedherein, a “conductive material” refers to a material having electricalconductivity greater than 1.0×10⁵ S/m. As used herein, an “insulatormaterial” or a “dielectric material” refers to a material havingelectrical conductivity less than 1.0×10⁻⁵ S/m. As used herein, a“heavily doped semiconductor material” refers to a semiconductormaterial that is doped with electrical dopant at a sufficiently highatomic concentration to become a conductive material either as formed asa crystalline material or if converted into a crystalline materialthrough an anneal process (for example, from an initial amorphousstate), i.e., to provide electrical conductivity greater than 1.0×10⁵S/m. A “doped semiconductor material” may be a heavily dopedsemiconductor material, or may be a semiconductor material that includeselectrical dopants (i.e., p-type dopants and/or n-type dopants) at aconcentration that provides electrical conductivity in the range from1.0×10⁻⁵ S/m to 1.0×10⁷ S/m. An “intrinsic semiconductor material”refers to a semiconductor material that is not doped with electricaldopants. Thus, a semiconductor material may be semiconducting orconductive, and may be an intrinsic semiconductor material or a dopedsemiconductor material. A doped semiconductor material may besemiconducting or conductive depending on the atomic concentration ofelectrical dopants therein. As used herein, a “metallic material” refersto a conductive material including at least one metallic elementtherein. All measurements for electrical conductivities are made at thestandard condition.

A monolithic three-dimensional memory array is one in which multiplememory levels are formed above a single substrate, such as asemiconductor wafer, with no intervening substrates. The term“monolithic” means that layers of each level of the array are directlydeposited on the layers of each underlying level of the array. Incontrast, two dimensional arrays may be formed separately and thenpackaged together to form a non-monolithic memory device. For example,non-monolithic stacked memories have been constructed by forming memorylevels on separate substrates and vertically stacking the memory levels,as described in U.S. Pat. No. 5,915,167 titled “Three-dimensionalStructure Memory.” The substrates may be thinned or removed from thememory levels before bonding, but as the memory levels are initiallyformed over separate substrates, such memories are not true monolithicthree-dimensional memory arrays. The substrate may include integratedcircuits fabricated thereon, such as driver circuits for a memory device

Generally, a semiconductor package (or a “package”) refers to a unitsemiconductor device that may be attached to a circuit board through aset of pins or solder balls. A semiconductor package may include asemiconductor chip (or a “chip”) or a plurality of semiconductor chipsthat are bonded to each other, for example, by flip-chip bonding oranother chip-to-chip bonding. A package or a chip may include a singlesemiconductor die (or a “die”) or a plurality of semiconductor dies. Adie is the smallest unit that may independently execute externalcommands or report status. Typically, a package or a chip with multipledies is capable of simultaneously executing as many number of externalcommands as the total number of dies therein. Each die includes one ormore planes. Identical concurrent operations may be executed in eachplane within a same die, although there may be some restrictions. Incase a die is a memory die, i.e., a die including memory elements,concurrent read operations, concurrent write operations, or concurrenterase operations may be performed in each plane within a same memorydie. In a memory die, each plane contains a number of memory blocks (or“blocks”), which are the smallest unit that may be erased by in a singleerase operation. Each memory block contains a number of pages, which arethe smallest units that may be selected for programming. A page is alsothe smallest unit that may be selected to a read operation.

Referring to FIGS. 1A-1F, an exemplary structure according to anembodiment of the present disclosure is illustrated. The exemplarystructure can include a semiconductor substrate on which atwo-dimensional array of semiconductor dies 900 is formed. Eachsemiconductor die 900 can have a same pattern as illustrated in FIG. 1A,which illustrates a layout of a single semiconductor die. Thesemiconductor die 900 can be a memory die including a plurality ofplanes, such as two to six planes, for example four planes asillustrated in FIG. 1A. Each plane may include a respective memory arrayregion 100 and at least one contact region 200, which may include arespective staircase region. Areas that are not employed for a memoryarray region 100 or a contact region 200 can be an area of a peripheralregion 300.

The exemplary structure includes a substrate 8 and semiconductor devices710 formed thereupon. The substrate 8 includes a substrate semiconductorlayer 9 at least at an upper portion thereof. Shallow trench isolationstructures 720 may be formed in an upper portion of the substratesemiconductor layer 9 to provide electrical isolation from othersemiconductor devices. The semiconductor devices 710 may include, forexample, field effect transistors including respective transistor activeregions 742 (i.e., source regions and drain regions), channel regions746, and gate structures 750. The field effect transistors may bearranged in a CMOS configuration. Each gate structure 750 may include,for example, a gate dielectric 752, a gate electrode 754, a dielectricgate spacer 756 and a gate cap dielectric 758. The semiconductor devices710 may include any semiconductor circuitry to support operation of amemory structure to be subsequently formed, which is typically referredto as a driver circuitry, which is also known as peripheral circuitry.As used herein, a peripheral circuitry refers to any, each, or all, ofword line decoder circuitry, word line switching circuitry, bit linedecoder circuitry, bit line sensing and/or switching circuitry, powersupply/distribution circuitry, data buffer and/or latch, or any othersemiconductor circuitry that may be implemented outside a memory arraystructure for a memory device. For example, the semiconductor devicesmay include word line switching devices for electrically biasing wordlines of three-dimensional memory structures to be subsequently formed.

Dielectric material layers are formed over the semiconductor devices,which are herein referred to as lower-level dielectric material layers760. The lower-level dielectric material layers 760 may include, forexample, a dielectric liner 762 (such as a silicon nitride liner thatblocks diffusion of mobile ions and/or apply appropriate stress tounderlying structures), first dielectric material layers 764 thatoverlie the dielectric liner 762, a silicon nitride layer (e.g.,hydrogen diffusion barrier) 766 that overlies the first dielectricmaterial layers 764, and at least one second dielectric layer 768.

The dielectric layer stack including the lower-level dielectric materiallayers 760 functions as a matrix for lower-level metal interconnectstructures 780 that provide electrical wiring to and from the variousnodes of the semiconductor devices and landing pads forthrough-memory-level contact via structures to be subsequently formed.The lower-level metal interconnect structures 780 are formed within thedielectric layer stack of the lower-level dielectric material layers760, and comprise a lower-level metal line structure located under andoptionally contacting a bottom surface of the silicon nitride layer 766.

For example, the lower-level metal interconnect structures 780 may beformed within the first dielectric material layers 764. The firstdielectric material layers 764 may be a plurality of dielectric materiallayers in which various elements of the lower-level metal interconnectstructures 780 are sequentially formed. Each dielectric material layerselected from the first dielectric material layers 764 may include anyof doped silicate glass, undoped silicate glass, organosilicate glass,silicon nitride, silicon oxynitride, and dielectric metal oxides (suchas aluminum oxide). In one embodiment, the first dielectric materiallayers 764 may comprise, or consist essentially of, dielectric materiallayers having dielectric constants that do not exceed the dielectricconstant of undoped silicate glass (silicon oxide) of 3.9. Thelower-level metal interconnect structures 780 may include various devicecontact via structures 782 (e.g., source and drain electrodes whichcontact the respective source and drain nodes of the device or gateelectrode contacts), intermediate lower-level metal line structures 784,lower-level metal via structures 786, and landing-pad-level metal linestructures 788 that are configured to function as landing pads forthrough-memory-level contact via structures to be subsequently formed.

The landing-pad-level metal line structures 788 may be formed within atopmost dielectric material layer of the first dielectric materiallayers 764 (which may be a plurality of dielectric material layers).Each of the lower-level metal interconnect structures 780 may include ametallic nitride liner and a metal fill structure. Top surfaces of thelanding-pad-level metal line structures 788 and the topmost surface ofthe first dielectric material layers 764 may be planarized by aplanarization process, such as chemical mechanical planarization. Thesilicon nitride layer 766 may be formed directly on the top surfaces ofthe landing-pad-level metal line structures 788 and the topmost surfaceof the first dielectric material layers 764.

The at least one second dielectric material layer 768 may include asingle dielectric material layer or a plurality of dielectric materiallayers. Each dielectric material layer selected from the at least onesecond dielectric material layer 768 may include any of doped silicateglass, undoped silicate glass, and organosilicate glass. In oneembodiment, the at least one first second material layer 768 maycomprise, or consist essentially of, dielectric material layers havingdielectric constants that do not exceed the dielectric constant ofundoped silicate glass (silicon oxide) of 3.9.

An optional layer of a metallic material and a layer of a semiconductormaterial may be deposited over, or within patterned recesses of, the atleast one second dielectric material layer 768, and is lithographicallypatterned to provide an optional conductive plate layer 6 and in-processsource-level material layers 110′. The optional conductive plate layer6, if present, provides a high conductivity conduction path forelectrical current that flows into, or out of, the in-processsource-level material layers 110′. The optional conductive plate layer 6includes a conductive material such as a metal or a heavily dopedsemiconductor material. The optional conductive plate layer 6, forexample, may include a tungsten layer having a thickness in a range from3 nm to 100 nm, although lesser and greater thicknesses may also beused. A metal nitride layer (not shown) may be provided as a diffusionbarrier layer on top of the conductive plate layer 6. The conductiveplate layer 6 may function as a special source line in the completeddevice. In addition, the conductive plate layer 6 may comprise an etchstop layer and may comprise any suitable conductive, semiconductor orinsulating layer. The optional conductive plate layer 6 may include ametallic compound material such as a conductive metallic nitride (e.g.,TiN) and/or a metal (e.g., W). The thickness of the optional conductiveplate layer 6 may be in a range from 5 nm to 100 nm, although lesser andgreater thicknesses may also be used.

The in-process source-level material layers 110′ may include variouslayers that are subsequently modified to form source-level materiallayers. The source-level material layers, upon formation, include asource contact layer that functions as a common source region forvertical field effect transistors of a three-dimensional memory device.In one embodiment, the in-process source-level material layers 110′ mayinclude, from bottom to top, a lower source-level semiconductor layer112, a lower sacrificial liner 103, a source-level sacrificial layer104, an upper sacrificial liner 105, an upper source-level semiconductorlayer 116, a source-level insulating layer 117, and asource-select-level semiconductor layer 118.

The lower source-level semiconductor layer 112 and the uppersource-level semiconductor layer 116 may include a doped semiconductormaterial such as doped polysilicon or doped amorphous silicon. Theconductivity type of the lower source-level semiconductor layer 112 andthe upper source-level semiconductor layer 116 may be the opposite ofthe conductivity of vertical semiconductor channels to be subsequentlyformed. For example, if the vertical semiconductor channels to besubsequently formed have a doping of a first conductivity type, thelower source-level semiconductor layer 112 and the upper source-levelsemiconductor layer 116 have a doping of a second conductivity type thatis the opposite of the first conductivity type. The thickness of each ofthe lower source-level semiconductor layer 112 and the uppersource-level semiconductor layer 116 may be in a range from 10 nm to 300nm, such as from 20 nm to 150 nm, although lesser and greaterthicknesses may also be used.

The source-level sacrificial layer 104 includes a sacrificial materialthat may be removed selective to the lower sacrificial liner 103 and theupper sacrificial liner 105. In one embodiment, the source-levelsacrificial layer 104 may include a semiconductor material such asundoped amorphous silicon or a silicon-germanium alloy with an atomicconcentration of germanium greater than 20%. The thickness of thesource-level sacrificial layer 104 may be in a range from 30 nm to 400nm, such as from 60 nm to 200 nm, although lesser and greaterthicknesses may also be used.

The lower sacrificial liner 103 and the upper sacrificial liner 105include materials that may function as an etch stop material duringremoval of the source-level sacrificial layer 104. For example, thelower sacrificial liner 103 and the upper sacrificial liner 105 mayinclude silicon oxide, silicon nitride, and/or a dielectric metal oxide.In one embodiment, each of the lower sacrificial liner 103 and the uppersacrificial liner 105 may include a silicon oxide layer having athickness in a range from 2 nm to 30 nm, although lesser and greaterthicknesses may also be used.

The source-level insulating layer 117 includes a dielectric materialsuch as silicon oxide. The thickness of the source-level insulatinglayer 117 may be in a range from 20 nm to 400 nm, such as from 40 nm to200 nm, although lesser and greater thicknesses may also be used. Thesource-select-level semiconductor layer 118 may include a conductivematerial that may be used as a source-select-level gate electrode. Forexample, the source-select-level semiconductor layer 118 may include adoped semiconductor material such as doped polysilicon or dopedamorphous silicon that may be subsequently converted into dopedpolysilicon by an anneal process. The thickness of thesource-select-level semiconductor layer 118 may be in a range from 30 nmto 200 nm, such as from 60 nm to 100 nm, although lesser and greaterthicknesses may also be used.

The in-process source-level material layers 110′ may be formed directlyabove a subset of the semiconductor devices on the substrate 8 (e.g.,silicon wafer). As used herein, a first element is located “directlyabove” a second element if the first element is located above ahorizontal plane including a topmost surface of the second element andan area of the first element and an area of the second element has anareal overlap in a plan view (i.e., along a vertical plane or directionperpendicular to the top surface of the substrate 8.

The optional conductive plate layer 6 and the in-process source-levelmaterial layers 110′ may be patterned to provide openings in areas inwhich through-memory-level contact via structures and through-dielectriccontact via structures are to be subsequently formed. Patterned portionsof the stack of the conductive plate layer 6 and the in-processsource-level material layers 110′ are present in each memory arrayregion 100 in which three-dimensional memory stack structures are to besubsequently formed.

The optional conductive plate layer 6 and the in-process source-levelmaterial layers 110′ may be patterned such that an opening extends overa staircase region 200 in which contact via structures contacting wordline electrically conductive layers are to be subsequently formed. Inone embodiment, the staircase region 200 may be laterally spaced fromthe memory array region 100 along a first horizontal direction hd1. Ahorizontal direction that is perpendicular to the first horizontaldirection hd1 is herein referred to as a second horizontal directionhd2. In one embodiment, additional openings in the optional conductiveplate layer 6 and the in-process source-level material layers 110′ maybe formed within the area of a memory array region 100, in which athree-dimensional memory array including memory stack structures is tobe subsequently formed. A peripheral device region 400 that issubsequently filled with a field dielectric material portion may beprovided adjacent to the staircase region 200.

The region of the semiconductor devices 710 and the combination of thelower-level dielectric material layers 760 and the lower-level metalinterconnect structures 780 is herein referred to an underlyingperipheral device region 700, which is located underneath a memory-levelassembly to be subsequently formed and includes peripheral devices forthe memory-level assembly. The lower-level metal interconnect structures780 are formed in the lower-level dielectric material layers 760.

The lower-level metal interconnect structures 780 may be electricallyconnected to active nodes (e.g., transistor active regions 742 or gateelectrodes 754) of the semiconductor devices 710 (e.g., CMOS devices),and are located at the level of the lower-level dielectric materiallayers 760. Through-memory-level contact via structures may besubsequently formed directly on the lower-level metal interconnectstructures 780 to provide electrical connection to memory devices to besubsequently formed. In one embodiment, the pattern of the lower-levelmetal interconnect structures 780 may be selected such that thelanding-pad-level metal line structures 788 (which are a subset of thelower-level metal interconnect structures 780 located at the topmostportion of the lower-level metal interconnect structures 780) mayprovide landing pad structures for the through-memory-level contact viastructures to be subsequently formed.

According to an aspect of the present disclosure, a topmost layer withinthe in-process source-level material layers 110′ can be patterned toform base bump portions 118P. As used herein, a “bump portion” refers toa material portion that protrudes above a planar top surface of asurrounding material portion. A bump portion may include the samematerial as the material layer having the planar top surface and may bea protruding portion of the material layer, or may include a differentmaterial than the material layer having the planar top surface. In otherwords, the bump portion may, or may not, be a portion of a materiallayer that provides the planar top surface above which the bump portionprotrudes. As used herein, a “base bump portion” refers to a bumpportion located at a bottom of a structure that includes additional bumpportions that overlie the bump portion. While the present disclosure isdescribed employing an embodiment in which the base bump portions 118Pare portions of the source-select-level semiconductor layer 118,embodiments are expressly contemplated herein in which the base bumpportions 118P are formed as portions of any topmost layer within thein-process source-level material layers 110′, or alternatively, arediscrete material portions that are deposited over the in-processsource-level material layers 110′ (e.g., in the bottom layer of analternating stack to be formed over the in-process source-level materiallayers 110′).

The base bump portions 118P may be formed by applying a photoresistlayer (not shown) over the in-process source-level material layers 110′or any additional material layer that is deposited over the in-processsource-level material layers 110′, lithographically patterning thephotoresist layer into discrete photoresist material portions that arelaterally spaced apart from each other with a lateral separationdistance in a range from 1 micron to 100 microns, such as from 30microns to 50 microns, and by anisotropically etching an upper portionof the topmost layer within the in-process source-level material layers110′ (such as the source-select-level semiconductor layer 118) or theadditional material layer. Each base bump portion 118P can have ahorizontal cross-sectional shape of a circle, a rectangle, a roundedrectangle, or any other two-dimensional curvilinear shape, and can havea maximum lateral dimension (such as a diameter or a diagonal of arectangular shape) in a range from 100 nm to 10 microns, such as 1micron to 5 microns, although lesser and greater maximum lateraldimensions may also be employed. The height of the base bump portions118P may be in a range from 50 nm to 1,000 nm, such as from 100 nm to500 nm, although lesser and greater thicknesses may also be employed. Inone embodiment, the thickness of the base bump portions 118P may begreater than the sum of a thickness of an insulating layer and athickness of a spacer material layer within an alternating stack ofinsulating layers and spacer material layers to be subsequentlydeposited thereupon. In one embodiment, the base bump portions 118P maybe semiconductor material portions that are portions of thesource-select-level semiconductor layer 118. Alternatively, the basebump portions 118P may be semiconductor material portions or dielectricmaterial portions including a different material than the material ofthe source-select-level semiconductor layer 118. In one embodiment, thebase bump portions 118P may be formed on, or in (i.e., as portions of),a semiconductor material layer such as the source-select-levelsemiconductor layer 118. In one embodiment, the base bump portions 118Pcomprise portions of a semiconductor material layer having a greaterthickness than portions of the semiconductor material layer that do notbelong to the base bump portions 118P. The base bump portions 118P mayhave straight vertical sidewalls or tapered sidewalls.

Referring to FIG. 2 , an alternating stack of first material layers andsecond material layers is subsequently formed. Each first material layermay include a first material, and each second material layer may includea second material that is different from the first material. In case atleast another alternating stack of material layers is subsequentlyformed over the alternating stack of the first material layers and thesecond material layers, the alternating stack is herein referred to as afirst-tier alternating stack. The level of the first-tier alternatingstack is herein referred to as a first-tier level, and the level of thealternating stack to be subsequently formed immediately above thefirst-tier level is herein referred to as a second-tier level, etc.

The first-tier alternating stack may include first insulting layers 132as the first material layers, and first spacer material layers as thesecond material layers. In one embodiment, the first spacer materiallayers may be sacrificial material layers that are subsequently replacedwith electrically conductive layers. In another embodiment, the firstspacer material layers may be electrically conductive layers that arenot subsequently replaced with other layers. While the presentdisclosure is described using embodiments in which sacrificial materiallayers are replaced with electrically conductive layers, embodiments inwhich the spacer material layers are formed as electrically conductivelayers (thereby obviating the need to perform replacement processes) areexpressly contemplated herein.

In one embodiment, the first material layers and the second materiallayers may be first insulating layers 132 and first sacrificial materiallayers 142, respectively. In one embodiment, each first insulating layer132 may include a first insulating material, and each first sacrificialmaterial layer 142 may include a first sacrificial material. Analternating plurality of first insulating layers 132 and firstsacrificial material layers 142 is formed over the in-processsource-level material layers 110′. As used herein, a “sacrificialmaterial” refers to a material that is removed during a subsequentprocessing step.

As used herein, an alternating stack of first elements and secondelements refers to a structure in which instances of the first elementsand instances of the second elements alternate. Each instance of thefirst elements that is not an end element of the alternating pluralityis adjoined by two instances of the second elements on both sides, andeach instance of the second elements that is not an end element of thealternating plurality is adjoined by two instances of the first elementson both ends. The first elements may have the same thickness throughout,or may have different thicknesses. The second elements may have the samethickness throughout, or may have different thicknesses. The alternatingplurality of first material layers and second material layers may beginwith an instance of the first material layers or with an instance of thesecond material layers, and may end with an instance of the firstmaterial layers or with an instance of the second material layers. Inone embodiment, an instance of the first elements and an instance of thesecond elements may form a unit that is repeated with periodicity withinthe alternating plurality.

The first-tier alternating stack (132, 142) may include first insulatinglayers 132 composed of the first material, and first sacrificialmaterial layers 142 composed of the second material, which is differentfrom the first material. The first material of the first insulatinglayers 132 may be at least one insulating material. Insulating materialsthat may be used for the first insulating layers 132 include, but arenot limited to silicon oxide (including doped or undoped silicateglass), silicon nitride, silicon oxynitride, organosilicate glass (OSG),spin-on dielectric materials, dielectric metal oxides that are commonlyknown as high dielectric constant (high-k) dielectric oxides (e.g.,aluminum oxide, hafnium oxide, etc.) and silicates thereof, dielectricmetal oxynitrides and silicates thereof, and organic insulatingmaterials. In one embodiment, the first material of the first insulatinglayers 132 may be silicon oxide.

The second material of the first sacrificial material layers 142 is asacrificial material that may be removed selective to the first materialof the first insulating layers 132. As used herein, a removal of a firstmaterial is “selective to” a second material if the removal processremoves the first material at a rate that is at least twice the rate ofremoval of the second material. The ratio of the rate of removal of thefirst material to the rate of removal of the second material is hereinreferred to as a “selectivity” of the removal process for the firstmaterial with respect to the second material.

The first sacrificial material layers 142 may comprise an insulatingmaterial, a semiconductor material, or a conductive material. The secondmaterial of the first sacrificial material layers 142 may besubsequently replaced with electrically conductive electrodes which mayfunction, for example, as control gate electrodes of a vertical NANDdevice. In one embodiment, the first sacrificial material layers 142 maybe material layers that comprise silicon nitride.

In one embodiment, the first insulating layers 132 may include siliconoxide, and sacrificial material layers may include silicon nitridesacrificial material layers. The first material of the first insulatinglayers 132 may be deposited, for example, by chemical vapor deposition(CVD). For example, if silicon oxide is used for the first insulatinglayers 132, tetraethylorthosilicate (TEOS) may be used as the precursormaterial for the CVD process. The second material of the firstsacrificial material layers 142 may be formed, for example, CVD oratomic layer deposition (ALD).

The thicknesses of the first insulating layers 132 and the firstsacrificial material layers 142 may be in a range from 20 nm to 50 nm,although lesser and greater thicknesses may be used for each firstinsulating layer 132 and for each first sacrificial material layer 142.The number of repetitions of the pairs of a first insulating layer 132and a first sacrificial material layer 142 may be in a range from 2 to1,024, and typically from 8 to 256, although a greater number ofrepetitions may also be used. In one embodiment, each first sacrificialmaterial layer 142 in the first-tier alternating stack (132, 142) mayhave a uniform thickness that is substantially invariant within eachrespective first sacrificial material layer 142.

A first insulating cap layer 170 is subsequently formed over thefirst-tier alternating stack (132, 142). The first insulating cap layer170 includes a dielectric material, which may be any dielectric materialthat may be used for the first insulating layers 132. In one embodiment,the first insulating cap layer 170 includes the same dielectric materialas the first insulating layers 132. The thickness of the firstinsulating cap layer 170 may be in a range from 20 nm to 300 nm,although lesser and greater thicknesses may also be used.

Generally, at least one alternating stack of insulating layers (such asthe first insulating layers 132) and spacer material layers (such as thefirst sacrificial material layers 142) can be formed over the array ofbase bump portions 118P. The spacer material layers may be formed as, ormay be subsequently replaced with, electrically conductive layers. Eachlayer among the first insulating layers 132 and the first spacermaterial layers (such as the first sacrificial material layers 142) canbe deposited by a respective conformal deposition process. Each layerwithin each alternating stack comprises a planar portion verticallyextending between a planar top surface and a planar bottom surface(i.e., a portion of which the topography is not affected by the basebump portions 118P) and bump portions (i.e., portions of which thetopography is affected by the presence of the base bump portions 118P).The bump portions of each layer within each alternating stack (such asthe bump portions of the first insulating layers 132 and the bumpportions of the second insulating layers 142) can overlie, and canoptionally conformally surround, a respective one of the base bumpportions 118P. Bump stack structures comprising a respective one of thebase bump portions 118P and a respective subset of the bump portions ofeach alternating stack (such as the first-tier alternating stackincluding the first insulating layers 132 and the first sacrificialmaterial layers 142) are formed.

Referring to FIGS. 3A-3C, the first insulating cap layer 170 and thefirst-tier alternating stack (132, 142) may be patterned to form firststepped surfaces in the staircase region 200. The staircase region 200may include a respective first stepped area in which the first steppedsurfaces are formed, and a second stepped area in which additionalstepped surfaces are to be subsequently formed in a second-tierstructure (to be subsequently formed over a first-tier structure) and/oradditional tier structures. The first stepped surfaces may be formed,for example, by forming a mask layer (not shown) with an openingtherein, etching a cavity within the levels of the first insulating caplayer 170, and iteratively expanding the etched area and verticallyrecessing the cavity by etching each pair of a first insulating layer132 and a first sacrificial material layer 142 located directlyunderneath the bottom surface of the etched cavity within the etchedarea. In one embodiment, top surfaces of the first sacrificial materiallayers 142 may be physically exposed at the first stepped surfaces. Thecavity overlying the first stepped surfaces is herein referred to as afirst stepped cavity.

A dielectric fill material (such as undoped silicate glass or dopedsilicate glass) may be deposited to fill the first stepped cavity.Excess portions of the dielectric fill material may be removed fromabove the horizontal plane including the top surface of the firstinsulating cap layer 170. A remaining portion of the dielectric fillmaterial that fills the region overlying the first stepped surfacesconstitute a first retro-stepped dielectric material portion 165. Asused herein, a “retro-stepped” element refers to an element that hasstepped surfaces and a horizontal cross-sectional area that increasesmonotonically as a function of a vertical distance from a top surface ofa substrate on which the element is present. The first-tier alternatingstack (132, 142) and the first retro-stepped dielectric material portion165 collectively constitute a first-tier structure, which is anin-process structure that is subsequently modified.

An inter-tier dielectric layer 180 may be optionally deposited over thefirst-tier structure (132, 142, 170, 165). The inter-tier dielectriclayer 180 includes a dielectric material such as silicon oxide. In oneembodiment, the inter-tier dielectric layer 180 may include a dopedsilicate glass having a greater etch rate than the material of the firstinsulating layers 132 (which may include an undoped silicate glass). Forexample, the inter-tier dielectric layer 180 may include phosphosilicateglass. The thickness of the inter-tier dielectric layer 180 may be in arange from 30 nm to 300 nm, although lesser and greater thicknesses mayalso be used.

A first patterning film 172 and a first etch mask layer 174 can bedeposited over the inter-dielectric layer 180. The first patterning film172 includes a material that can assist in providing straight verticalprofiles for openings to be subsequently formed through the first-tieralternating stack (132, 142). In one embodiment, the first patterningfilm 172 can include a carbon-based material such as amorphous carbon ordiamond-like carbon. For example, Advanced Patterning Film™ (APF)available from Applied Materials Inc.™ may be employed for the firstpatterning film. The thickness of the first patterning film 172 may bein a range from 300 nm to 1 micron, although lesser and greaterthicknesses may also be employed. The first etch mask layer 174 isoptional, and may include a dielectric antireflective coating (DARC)comprising an inorganic dielectric material, such as silicon oxide orsilicon nitride, or a semiconductor material such as polysilicon. Thethickness of the first etch mask layer 174 may be in a range from 100 nmto 300 nm, although lesser and greater thicknesses may also be employed.

Each of the first insulating layers 132 and first sacrificial materiallayers 142 comprises a planar portion (PP) located between a planar topsurface and a planar bottom surface and bump portions (BP) that areadjoined to the planar portion at a respective periphery P. The planarportion of each layer is located between areas of the topographicalbumps caused by the presence of the base bump portions 118P. Each bumpportion BP of the layers (132, 142) has a respective raised top surfacethat is vertically raised from the planar top surface of the planarportion PP the respective layer (132, 142) and a respective raisedbottom surface that is raised from the planar bottom surface of therespective layer (132, 142).

Each combination of material portions that replicate topographicalfeatures of a base bump portion 118P constitutes a bump stack structureBSS. Each bump stack structure BSS includes a base bump portion 118Plocated underneath the first-tier alternating stack (132, 142) and arespective subset of the bump portions BP of the first-tier alternatingstack (132, 142) that overlie or underlie one another. Each overlyingperiphery P within the respective subset of bump portions BP islaterally offset outward from any underlying periphery P within therespective subset of the bump portions BP.

For each layer of the first insulating layers 132 and the first spacermaterial layers (such as the first sacrificial material layers 142), thebump portions BP and the planar portion PP have a same thickness. In oneembodiment, a volume ratio of the planar portion PP to the bump portionBP in each of the insulating layers 132 and the sacrificial materiallayers 142 is greater than 0.8 and less than 1.

In one embodiment, each bump portion BP of a layer within the first-tieralternating stack (132, 142) comprises a respective bottom edge at whichthe planar bottom surface of the layer adjoins a first tapered orvertical surface of the layer, and a respective top edge at which theplanar top surface of the layer adjoins a second tapered or verticalsurface of the layer. In one embodiment, the respective top edge islaterally offset outward from the respective bottom edge by a uniformlateral offset distance in a plan view. In one embodiment, the uniformlateral offset distance is in a range from 80% to 100% of a thickness ofthe layer within the insulating layers 132 and the spacer materiallayers 142.

In one embodiment shown in FIG. 3C, within each of the bump stackstructures BSS, each overlying periphery P within the respective subsetof bump portions BP is laterally offset outward from any underlyingperiphery within the respective subset of the bump portions BP. In otherwords, the bump portion BP in a given layer in the alternating stack iswider than the underlying bump portion BP of an underlying layer in thesame alternating stack. The layers (132 142) of the alternating stackmay be inclined at an angle of about 30 to 90, such as about 45 degreesat the periphery P of the bump portions BP. In one embodiment, the bumpstack structures BSS vertically extends from a bottommost layer withinthe first-tier alternating stack (132, 142) to a topmost layer withinthe first-tier alternating stack (132, 142).

Referring to FIGS. 4A-4C, a first bottom antireflective coating (BARC)layer 176 and a first photoresist layer 177 can be applied over theexemplary structure. The first BARC layer 176 includes aself-planarizing antireflective coating material, and can have athickness greater than the thickness of the base bump portions 118P.Thus, the top surface of the first BARC layer 176 can be planar.

Referring to FIGS. 5A and 5B, the photoresist layer 177 islithographically patterned to form various openings therethrough. Thepattern of openings in the photoresist layer 177 can be transferredthrough the first BARC layer 176, the first etch mask layer 174, thefirst patterning film 172, the inter-tier dielectric layer 180 and thefirst-tier structure (132, 142, 170, 165) and into the in-processsource-level material layers 110′ by a first anisotropic etch process toform the various first-tier openings (149, 129) concurrently, i.e.,during the first isotropic etch process. Various first-tier openings(149, 129) may be formed through the inter-tier dielectric layer 180 andthe first-tier structure (132, 142, 170, 165) and into the in-processsource-level material layers 110′. The various first-tier openings (149,129) may include first-tier memory openings 149 and first-tier supportopenings 129. Locations of steps S in the first-tier alternating stack(132, 142) are illustrated as dotted lines in FIG. 5B. The photoresistlayer 177, the first BARC layer 176, the first etch mask layer 174 canbe subsequently removed.

The first-tier memory openings 149 are openings that are formed in thememory array region 100 through each layer within the first-tieralternating stack (132, 142) and are subsequently used to form memorystack structures therein. The first-tier memory openings 149 may beformed in clusters of first-tier memory openings 149 that are laterallyspaced apart along the second horizontal direction hd2. Each cluster offirst-tier memory openings 149 may be formed as a two-dimensional arrayof first-tier memory openings 149. The first-tier memory openings 149may extend through both the bump portion BP of the bump stack structuresBSS and through the planar portions PP of the layers of the alternatingstack.

The first-tier support openings 129 are openings that are formed in thestaircase region 200, and are subsequently employed to form supportpillar structures. A subset of the first-tier support openings 129 thatis formed through the first retro-stepped dielectric material portion165 may be formed through a respective horizontal surface of the firststepped surfaces.

In one embodiment, the first anisotropic etch process may include aninitial step in which the materials of the first-tier alternating stack(132, 142) are etched concurrently with the material of the firstretro-stepped dielectric material portion 165. The chemistry of theinitial etch step may alternate to optimize etching of the first andsecond materials in the first-tier alternating stack (132, 142) whileproviding a comparable average etch rate to the material of the firstretro-stepped dielectric material portion 165. The first anisotropicetch process may use, for example, a series of reactive ion etchprocesses or a single reaction etch process (e.g., CF₄/O₂/Ar etch). Thesidewalls of the various first-tier openings (149, 129) may besubstantially vertical, or may be tapered.

After etching through the alternating stack (132, 142) and the firstretro-stepped dielectric material portion 165, the chemistry of aterminal portion of the first anisotropic etch process may be selectedto etch through the dielectric material(s) of the at least one seconddielectric layer 768 with a higher etch rate than an average etch ratefor the in-process source-level material layers 110′. For example, theterminal portion of the anisotropic etch process may include a step thatetches the dielectric material(s) of the at least one second dielectriclayer 768 selective to a semiconductor material within a component layerin the in-process source-level material layers 110′. In one embodiment,the terminal portion of the first anisotropic etch process may etchthrough the source-select-level semiconductor layer 118, thesource-level insulating layer 117, the upper source-level semiconductorlayer 116, the upper sacrificial liner 105, the source-level sacrificiallayer 104, and the lower sacrificial liner 103, and at least partly intothe lower source-level semiconductor layer 112. The terminal portion ofthe first anisotropic etch process may include at least one etchchemistry for etching the various semiconductor materials of thein-process source-level material layers 110′. The photoresist layer maybe subsequently removed, for example, by ashing.

Optionally, the portions of the first-tier memory openings 149 and thefirst-tier support openings 129 at the level of the inter-tierdielectric layer 180 may be laterally expanded by an isotropic etch. Inthis case, the inter-tier dielectric layer 180 may comprise a dielectricmaterial (such as borosilicate glass) having a greater etch rate thanthe first insulating layers 132 (that may include undoped silicateglass) in dilute hydrofluoric acid. An isotropic etch (such as a wetetch using HF) may be used to expand the lateral dimensions of thefirst-tier memory openings 149 at the level of the inter-tier dielectriclayer 180. The portions of the first-tier memory openings 149 located atthe level of the inter-tier dielectric layer 180 may be optionallywidened to provide a larger landing pad for second-tier memory openingsto be subsequently formed through a second-tier alternating stack (to besubsequently formed prior to formation of the second-tier memoryopenings).

Referring to FIG. 6 , sacrificial first-tier opening fill portions (148,128) may be formed in the various first-tier openings (149, 129). Forexample, a sacrificial first-tier fill material is depositedconcurrently deposited in each of the first-tier openings (149, 129).The sacrificial first-tier fill material includes a material that may besubsequently removed selective to the materials of the first insulatinglayers 132 and the first sacrificial material layers 142.

In one embodiment, the sacrificial first-tier fill material may includea semiconductor material such as silicon (e.g., a-Si or polysilicon), asilicon-germanium alloy, germanium, a III-V compound semiconductormaterial, or a combination thereof. Optionally, a thin etch stop liner(such as a silicon oxide layer or a silicon nitride layer having athickness in a range from 1 nm to 3 nm) may be used prior to depositingthe sacrificial first-tier fill material. The sacrificial first-tierfill material may be formed by a non-conformal deposition or a conformaldeposition method.

In another embodiment, the sacrificial first-tier fill material mayinclude a silicon oxide material having a higher etch rate than thematerials of the first insulating layers 132, the first insulating caplayer 170, and the inter-tier dielectric layer 180. For example, thesacrificial first-tier fill material may include borosilicate glass orporous or non-porous organosilicate glass having an etch rate that is atleast 100 times higher than the etch rate of densified TEOS oxide (i.e.,a silicon oxide material formed by decomposition oftetraethylorthosilicate glass in a chemical vapor deposition process andsubsequently densified in an anneal process) in a 100:1 dilutehydrofluoric acid. In this case, a thin etch stop liner (such as asilicon nitride layer having a thickness in a range from 1 nm to 3 nm)may be used prior to depositing the sacrificial first-tier fillmaterial. The sacrificial first-tier fill material may be formed by anon-conformal deposition or a conformal deposition method.

In yet another embodiment, the sacrificial first-tier fill material mayinclude amorphous silicon or a carbon-containing material (such asamorphous carbon or diamond-like carbon) that may be subsequentlyremoved by ashing, or a silicon-based polymer that may be subsequentlyremoved selective to the materials of the first-tier alternating stack(132, 142).

Portions of the deposited sacrificial material may be removed from abovethe topmost layer of the first-tier alternating stack (132, 142), suchas from above the inter-tier dielectric layer 180. For example, thesacrificial first-tier fill material may be recessed to a top surface ofthe inter-tier dielectric layer 180 using a planarization process. Theplanarization process may include a recess etch, chemical mechanicalplanarization (CMP), or a combination thereof. The top surface of theinter-tier dielectric layer 180 may be used as an etch stop layer or aplanarization stop layer.

Remaining portions of the sacrificial first-tier fill material comprisesacrificial first-tier opening fill portions (148, 128). Specifically,each remaining portion of the sacrificial material in a first-tiermemory opening 149 constitutes a sacrificial first-tier memory openingfill portion 148. Each remaining portion of the sacrificial material ina first-tier support opening 129 constitutes a sacrificial first-tiersupport opening fill portion 128. The various sacrificial first-tieropening fill portions (148, 128) are concurrently formed, i.e., during asame set of processes including the deposition process that deposits thesacrificial first-tier fill material and the planarization process thatremoves the first-tier deposition process from above the first-tieralternating stack (132, 142) (such as from above the top surface of theinter-tier dielectric layer 180). The top surfaces of the sacrificialfirst-tier opening fill portions (148, 128) may be coplanar with the topsurface of the inter-tier dielectric layer 180. Each of the sacrificialfirst-tier opening fill portions (148, 128) may, or may not, includecavities therein.

Referring to FIGS. 7A-7C, a second-tier structure may be formed over thefirst-tier structure (132, 142, 170, 148). The second-tier structure mayinclude an additional alternating stack of insulating layers and spacermaterial layers, which may be sacrificial material layers. For example,a second alternating stack (232, 242) of material layers may besubsequently formed on the top surface of the first-tier alternatingstack (132, 142). The second alternating stack (232, 242) includes analternating plurality of third material layers and fourth materiallayers. Each third material layer may include a third material, and eachfourth material layer may include a fourth material that is differentfrom the third material. In one embodiment, the third material may bethe same as the first material of the first insulating layer 132, andthe fourth material may be the same as the second material of the firstsacrificial material layers 142.

In one embodiment, the third material layers may be second insulatinglayers 232 and the fourth material layers may be second spacer materiallayers that provide vertical spacing between each vertically neighboringpair of the second insulating layers 232. In one embodiment, the thirdmaterial layers and the fourth material layers may be second insulatinglayers 232 and second sacrificial material layers 242, respectively. Thethird material of the second insulating layers 232 may be at least oneinsulating material. The fourth material of the second sacrificialmaterial layers 242 may be a sacrificial material that may be removedselective to the third material of the second insulating layers 232. Thesecond sacrificial material layers 242 may comprise an insulatingmaterial, a semiconductor material, or a conductive material. The fourthmaterial of the second sacrificial material layers 242 may besubsequently replaced with electrically conductive electrodes which mayfunction, for example, as control gate electrodes of a vertical NANDdevice.

In one embodiment, each second insulating layer 232 may include a secondinsulating material, and each second sacrificial material layer 242 mayinclude a second sacrificial material. In this case, the secondalternating stack (232, 242) may include an alternating plurality ofsecond insulating layers 232 and second sacrificial material layers 242.The third material of the second insulating layers 232 may be deposited,for example, by chemical vapor deposition (CVD). The fourth material ofthe second sacrificial material layers 242 may be formed, for example,CVD or atomic layer deposition (ALD).

The third material of the second insulating layers 232 may be at leastone insulating material. Insulating materials that may be used for thesecond insulating layers 232 may be any material that may be used forthe first insulating layers 132. The fourth material of the secondsacrificial material layers 242 is a sacrificial material that may beremoved selective to the third material of the second insulating layers232. Sacrificial materials that may be used for the second sacrificialmaterial layers 242 may be any material that may be used for the firstsacrificial material layers 142. In one embodiment, the secondinsulating material may be the same as the first insulating material,and the second sacrificial material may be the same as the firstsacrificial material.

The thicknesses of the second insulating layers 232 and the secondsacrificial material layers 242 may be in a range from 20 nm to 50 nm,although lesser and greater thicknesses may be used for each secondinsulating layer 232 and for each second sacrificial material layer 242.The number of repetitions of the pairs of a second insulating layer 232and a second sacrificial material layer 242 may be in a range from 2 to1,024, and typically from 8 to 256, although a greater number ofrepetitions may also be used. In one embodiment, each second sacrificialmaterial layer 242 in the second alternating stack (232, 242) may have auniform thickness that is substantially invariant within each respectivesecond sacrificial material layer 242.

Second stepped surfaces in the second stepped area may be formed in thestaircase region 200 using a same set of processing steps as theprocessing steps used to form the first stepped surfaces in the firststepped area with suitable adjustment to the pattern of at least onemasking layer. A second retro-stepped dielectric material portion 265may be formed over the second stepped surfaces in the staircase region200.

A second insulating cap layer 270 may be subsequently formed over thesecond alternating stack (232, 242). The second insulating cap layer 270includes a dielectric material that is different from the material ofthe second sacrificial material layers 242. In one embodiment, thesecond insulating cap layer 270 may include silicon oxide. In oneembodiment, the first and second sacrificial material layers (142, 242)may comprise silicon nitride.

Generally speaking, at least one alternating stack of insulating layers(132, 232) and spacer material layers (such as sacrificial materiallayers (142, 242)) may be formed over the in-process source-levelmaterial layers 110′, and at least one retro-stepped dielectric materialportion (165, 265) may be formed over the staircase regions on the atleast one alternating stack (132, 142, 232, 242).

Optionally, drain-select-level isolation structures 72 may be formedthrough a subset of layers in an upper portion of the second-tieralternating stack (232, 242). The second sacrificial material layers 242that are cut by the drain-select-level isolation structures 72correspond to the levels in which drain-select-level electricallyconductive layers are subsequently formed. The drain-select-levelisolation structures 72 include a dielectric material such as siliconoxide. The drain-select-level isolation structures 72 may laterallyextend along a first horizontal direction hd1, and may be laterallyspaced apart along a second horizontal direction hd2 that isperpendicular to the first horizontal direction hd1. The combination ofthe second alternating stack (232, 242), the second retro-steppeddielectric material portion 265, the second insulating cap layer 270,and the optional drain-select-level isolation structures 72 collectivelyconstitute a second-tier structure (232, 242, 265, 270, 72).

Each layer of the second insulating layers 232 and the second spacermaterial layers (such as the second sacrificial material layers 242) canbe deposited by a respective conformal deposition process. Each of thesecond insulating layers 232 and second sacrificial material layers 242comprises a planar portion PP located between a planar top surface and aplanar bottom surface and bump portions BP that are adjoined to theplanar portion PP at a respective periphery P. The planar portion ofeach layer is located between areas of the topographical bumps caused bythe presence of the base bump portions 118P. Each bump portion BP of thelayers has a respective raised top surface that is vertically raisedfrom the planar top surface of the planar portion PP of the respectivelayer and a respective raised bottom surface that is raised from theplanar bottom surface of the respective layer.

Each combination of material portions that replicate topographicalfeatures of a base bump portion 118P constitutes a bump stack structureBSS. Each bump stack structure BSS includes a base bump portion 118Plocated underneath the first-tier alternating stack (132, 142) and arespective subset of the bump portions BP of the alternating stacks{(132, 142), (232, 242)} that overlie or underlie one another andoverlie the base bump portion 118P. Each overlying periphery P withinthe respective subset of bump portions BP is laterally offset outwardfrom any underlying periphery P within the respective subset of the bumpportions BP.

For each layer of the second insulating layers 232 and the second spacermaterial layers (such as the second sacrificial material layers 242),the bump portions BP and the planar portion PP have a same thickness. Inone embodiment, a volume ratio of the planar portion PP to the bumpportion BP in each of the second insulating layers 232 and the secondsacrificial material layers 242 is greater than 0.8 and less than 1.

In one embodiment, each bump portion BP of a layer within thesecond-tier alternating stack (232, 242) comprises a respective bottomedge at which the planar bottom surface of the layer adjoins a secondtapered or vertical surface of the layer, and a respective top edge atwhich the planar top surface of the layer adjoins a second tapered orvertical surface of the layer. In one embodiment, the respective topedge is laterally offset outward from the respective bottom edge by auniform lateral offset distance in a plan view. In one embodiment, theuniform lateral offset distance is in a range from 80% to 100% of athickness of the layer within the second insulating layers and thesecond spacer material layers.

In one embodiment, within each of the bump stack structure BSS, eachoverlying periphery P within the respective subset of bump portions BPis laterally offset outward from any underlying periphery within therespective subset of the bump portions BP. In one embodiment, the bumpstack structures BSS vertically extends from a bottommost layer withinthe first-tier alternating stack (132, 142) to a topmost layer withinthe second-tier alternating stack (232, 242).

The second insulating cap layer 270 includes insulating cap bumpportions 270P1 that are portions of the bump stack structures BSS andare located over the base bump portions 118P. According to an aspect ofthe present disclosure, the second insulating cap layer 270 can bepatterned to form protrusion structures 270P2 over the alternatingstacks {(132, 142), (232, 242)} in areas that are laterally spaced fromthe bump stack structures BSS. For example, a photoresist layer (notshown) can be applied over the second insulating cap layer to coverdiscrete areas located outside the areas of the bump stack structuresBSS, and portions of the second insulating cap layer 270 that are notmasked by the photoresist layer can be recessed, for example, by ananisotropic etch process. The photoresist layer can be subsequentlyremoved. The protrusion structures 270P2 can be the portions of thesecond insulating cap layer 270 that are not recessed by the anisotropicetch process. Generally, the protrusion structures 270P2 can be formedby depositing and patterning an insulating cap layer over at least onealternating stack {(131, 142), (232, 242)}. The protrusion structures270P2 comprise portions of the insulating cap layer having a greaterthickness than portions of the insulating cap layer that do not belongto the protrusion structures 270P2. The bump stack structures BSS andthe protrusion structures 270P2 can be subsequently employed to measurein-die deformation (i.e., intra-die overlay) during subsequentprocesses.

Referring to FIGS. 8A-8C, a second patterning film 272 and a second etchmask layer 274 can be deposited over the second insulating cap layer270. The second patterning film 272 includes a material that can assistin providing straight vertical profiles for openings to be subsequentlyformed through the second-tier alternating stack (232, 242). In oneembodiment, the second patterning film 272 can include a carbon-basedmaterial such as amorphous carbon or diamond-like carbon. For example,Advanced Patterning Film™ (APF) available from Applied Materials Inc.™may be employed for the second patterning film. The thickness of thesecond patterning film 272 may be in a range from 300 nm to 1 micron,although lesser and greater thicknesses may also be employed. The secondetch mask layer 274 is optional, and may include a DARC layer comprisingan inorganic dielectric material such as silicon oxide or siliconnitride, or a semiconductor material such as polysilicon. The thicknessof the second etch mask layer 274 may be in a range from 100 nm to 300nm, although lesser and greater thicknesses may also be employed. Thebump stack structures BSS and the protrusion structures PS propagateinto the second patterning film 272 and a second etch mask layer 274.

Referring to FIGS. 9A and 9B, various second-tier openings (249, 229)may be formed through the second-tier structure (232, 242, 265, 270,72). A photoresist layer (not shown) may be applied over the second etchmask layer 274, second patterning film 272 and the second insulating caplayer 270, and may be lithographically patterned to form variousopenings therethrough. The pattern of the openings may be the same asthe pattern of the various first-tier openings (149, 129), which is thesame as the sacrificial first-tier opening fill portions (148, 128).Thus, the lithographic mask used to pattern the first-tier openings(149, 129) may be used to pattern the photoresist layer. The bump stackstructures BSS and the protrusion structures PS propagate into thephotoresist layer. The deformation within the alternating stacks {(132,142), (232, 242)} can be measured by measuring lateral distances betweenpairs of a respective one of bump stack structures BSS and a respectiveone of the protrusion structures PS using imaging based overlay (IBO).The IBO process is faster than using prior art scanning electronmicroscopy (SEM) to find alignment marks. The deformation may be causedby different amount of stress between the first tier and the secondtier, which leads to an intra-die 900 overlay error. Thephotolithography process can be adjusted (e.g., by selecting thicknessesof layers 172, 174, 176, 274, and/or 276 to avoid defocusing) tocompensate for the measured deformation, thus reducing the overlayererrors between the first and second tiers.

The pattern of openings in the photoresist layer may be transferredthrough the second-tier structure (232, 242, 265, 270, 72) by a secondanisotropic etch process to form various second-tier openings (249, 229)concurrently, i.e., during the second anisotropic etch process. Thevarious second-tier openings (249, 229) may include second-tier memoryopenings 249 and second-tier support openings 229.

The second-tier memory openings 249 are formed directly on a top surfaceof a respective one of the sacrificial first-tier memory opening fillportions 148. The second-tier support openings 229 are formed directlyon a top surface of a respective one of the sacrificial first-tiersupport opening fill portions 128. Further, each second-tier supportopenings 229 may be formed through a horizontal surface within thesecond stepped surfaces, which include the interfacial surfaces betweenthe second alternating stack (232, 242) and the second retro-steppeddielectric material portion 265. Locations of steps S in the first-tieralternating stack (132, 142) and the second-tier alternating stack (232,242) are illustrated as dotted lines in FIG. 7B.

The second anisotropic etch process may include an etch step in whichthe materials of the second-tier alternating stack (232, 242) are etchedconcurrently with the material of the second retro-stepped dielectricmaterial portion 265. The chemistry of the etch step may alternate tooptimize etching of the materials in the second-tier alternating stack(232, 242) while providing a comparable average etch rate to thematerial of the second retro-stepped dielectric material portion 265.The second anisotropic etch process may use, for example, a series ofreactive ion etch processes or a single reaction etch process (e.g.,CF₄/O₂/Ar etch). The sidewalls of the various second-tier openings (249,229) may be substantially vertical, or may be tapered. A bottomperiphery of each second-tier opening (249, 229) may be laterallyoffset, and/or may be located entirely within, a periphery of a topsurface of an underlying sacrificial first-tier opening fill portion(148, 128). The photoresist layer may be subsequently removed, forexample, by ashing.

Referring to FIG. 10 , the sacrificial first-tier fill material of thesacrificial first-tier opening fill portions (148, 128) may be removedusing an etch process that etches the sacrificial first-tier fillmaterial selective to the materials of the first and second insulatinglayers (132, 232), the first and second sacrificial material layers(142,242), the first and second insulating cap layers (170, 270), andthe inter-tier dielectric layer 180. A memory opening 49, which is alsoreferred to as an inter-tier memory opening 49, is formed in eachcombination of a second-tier memory openings 249 and a volume from whicha sacrificial first-tier memory opening fill portion 148 is removed. Asupport opening 19, which is also referred to as an inter-tier supportopening 19, is formed in each combination of a second-tier supportopenings 229 and a volume from which a sacrificial first-tier supportopening fill portion 128 is removed.

Formation of openings (49, 19) through the alternating stacks {(132,142), (232, 242)} results in uneven removal of materials across thesemiconductor die 900 because the openings (49, 19) are formed primarilywithin the memory array regions 100 and the contact regions 200.According to an aspect of the present disclosure, deformation within thealternating stacks {(132, 142), (232, 242)} can be measured by measuringlateral distances between pairs of a respective one of bump stackstructures BSS and a respective one of the protrusion structures PS,which function as alignment marks. Thus, overlay errors in each memoryarray region 100 in each die may be measured and the lithography processmay be adjusted to compensate for these overlay errors. In contrast,alignment marks located in the kerf area of the substrate outside thememory array regions 100 may not be sufficient to detect and measuresuch intra-die overlay errors. Furthermore, such alignment marks in thekerf area may be omitted in some embodiments such that more substratearea is used for the memory die 900.

FIGS. 11A-11D provide sequential cross-sectional views of a memoryopening 49 during formation of a memory pillar structure. The samestructural change occurs in each of the memory openings 49 and thesupport openings 19.

Referring to FIG. 11A, a memory opening 49 in the first exemplary devicestructure of FIG. 8 is illustrated. The memory opening 49 extendsthrough the first-tier structure and the second-tier structure.

Referring to FIG. 11B, a stack of layers including a blocking dielectriclayer 52, a charge storage layer 54, a tunneling dielectric layer 56,and a semiconductor channel material layer 60L may be sequentiallydeposited in the memory openings 49. The blocking dielectric layer 52may include a single dielectric material layer or a stack of a pluralityof dielectric material layers. In one embodiment, the blockingdielectric layer may include a dielectric metal oxide layer consistingessentially of a dielectric metal oxide. As used herein, a dielectricmetal oxide refers to a dielectric material that includes at least onemetallic element and at least oxygen. The dielectric metal oxide mayconsist essentially of the at least one metallic element and oxygen, ormay consist essentially of the at least one metallic element, oxygen,and at least one non-metallic element such as nitrogen. In oneembodiment, the blocking dielectric layer 52 may include a dielectricmetal oxide having a dielectric constant greater than 7.9, i.e., havinga dielectric constant greater than the dielectric constant of siliconnitride. The thickness of the dielectric metal oxide layer may be in arange from 1 nm to 20 nm, although lesser and greater thicknesses mayalso be used. The dielectric metal oxide layer may subsequently functionas a dielectric material portion that blocks leakage of storedelectrical charges to control gate electrodes. In one embodiment, theblocking dielectric layer 52 includes aluminum oxide. Alternatively oradditionally, the blocking dielectric layer 52 may include a dielectricsemiconductor compound such as silicon oxide, silicon oxynitride,silicon nitride, or a combination thereof.

Subsequently, the charge storage layer 54 may be formed. In oneembodiment, the charge storage layer 54 may be a continuous layer orpatterned discrete portions of a charge trapping material including adielectric charge trapping material, which may be, for example, siliconnitride. Alternatively, the charge storage layer 54 may include acontinuous layer or patterned discrete portions of a conductive materialsuch as doped polysilicon or a metallic material that is patterned intomultiple electrically isolated portions (e.g., floating gates), forexample, by being formed within lateral recesses into sacrificialmaterial layers (142, 242). In one embodiment, the charge storage layer54 includes a silicon nitride layer. In one embodiment, the sacrificialmaterial layers (142, 242) and the insulating layers (132, 232) may havevertically coincident sidewalls, and the charge storage layer 54 may beformed as a single continuous layer. Alternatively, the sacrificialmaterial layers (142, 242) may be laterally recessed with respect to thesidewalls of the insulating layers (132, 232), and a combination of adeposition process and an anisotropic etch process may be used to formthe charge storage layer 54 as a plurality of memory material portionsthat are vertically spaced apart. The thickness of the charge storagelayer 54 may be in a range from 2 nm to 20 nm, although lesser andgreater thicknesses may also be used.

The tunneling dielectric layer 56 includes a dielectric material throughwhich charge tunneling may be performed under suitable electrical biasconditions. The charge tunneling may be performed through hot-carrierinjection or by Fowler-Nordheim tunneling induced charge transferdepending on the mode of operation of the monolithic three-dimensionalNAND string memory device to be formed. The tunneling dielectric layer56 may include silicon oxide, silicon nitride, silicon oxynitride,dielectric metal oxides (such as aluminum oxide and hafnium oxide),dielectric metal oxynitride, dielectric metal silicates, alloys thereof,and/or combinations thereof. In one embodiment, the tunneling dielectriclayer 56 may include a stack of a first silicon oxide layer, a siliconoxynitride layer, and a second silicon oxide layer, which is commonlyknown as an ONO stack. In one embodiment, the tunneling dielectric layer56 may include a silicon oxide layer that is substantially free ofcarbon or a silicon oxynitride layer that is substantially free ofcarbon. The thickness of the tunneling dielectric layer 56 may be in arange from 2 nm to 20 nm, although lesser and greater thicknesses mayalso be used. The stack of the blocking dielectric layer 52, the chargestorage layer 54, and the tunneling dielectric layer 56 constitutes amemory film 50 that stores memory bits.

The semiconductor channel material layer 60L includes a p-dopedsemiconductor material such as at least one elemental semiconductormaterial, at least one III-V compound semiconductor material, at leastone II-VI compound semiconductor material, at least one organicsemiconductor material, or other semiconductor materials known in theart. In one embodiment, the semiconductor channel material layer 60L mayhaving a uniform doping. In one embodiment, the semiconductor channelmaterial layer 60L has a p-type doping in which p-type dopants (such asboron atoms) are present at an atomic concentration in a range from1.0×10¹²/cm³ to 1.0×10¹⁸/cm³, such as from 1.0×10¹⁴/cm³ to 1.0×10¹⁷/cm³.In one embodiment, the semiconductor channel material layer 60Lincludes, and/or consists essentially of, boron-doped amorphous siliconor boron-doped polysilicon. In another embodiment, the semiconductorchannel material layer 60L has an n-type doping in which n-type dopants(such as phosphor atoms or arsenic atoms) are present at an atomicconcentration in a range from 1.0×10¹²/cm³ to 1.0×10¹⁸/cm³, such as from1.0×10¹⁴/cm³ to 1.0×10¹⁷/cm³. The semiconductor channel material layer60L may be formed by a conformal deposition method such as low pressurechemical vapor deposition (LPCVD). The thickness of the semiconductorchannel material layer 60L may be in a range from 2 nm to 10 nm,although lesser and greater thicknesses may also be used. A cavity 49′is formed in the volume of each memory opening 49 that is not filledwith the deposited material layers (52, 54, 56, 60L).

Referring to FIG. 11C, in case the cavity 49′ in each memory opening isnot completely filled by the semiconductor channel material layer 60L, adielectric core layer may be deposited in the cavity 49′ to fill anyremaining portion of the cavity 49′ within each memory opening. Thedielectric core layer includes a dielectric material such as siliconoxide or organosilicate glass. The dielectric core layer may bedeposited by a conformal deposition method such as low pressure chemicalvapor deposition (LPCVD), or by a self-planarizing deposition processsuch as spin coating. The horizontal portion of the dielectric corelayer overlying the second insulating cap layer 270 may be removed, forexample, by a recess etch. The recess etch continues until top surfacesof the remaining portions of the dielectric core layer are recessed to aheight between the top surface of the second insulating cap layer 270and the bottom surface of the second insulating cap layer 270. Eachremaining portion of the dielectric core layer constitutes a dielectriccore 62.

Referring to FIG. 11D, a doped semiconductor material having a doping ofa second conductivity type may be deposited in cavities overlying thedielectric cores 62. The second conductivity type is the opposite of thefirst conductivity type. For example, if the first conductivity type isp-type, the second conductivity type is n-type, and vice versa. Portionsof the deposited doped semiconductor material, the semiconductor channelmaterial layer 60L, the tunneling dielectric layer 56, the chargestorage layer 54, and the blocking dielectric layer 52 that overlie thehorizontal plane including the top surface of the second insulating caplayer 270 may be removed by a planarization process such as a chemicalmechanical planarization (CMP) process.

Each remaining portion of the doped semiconductor material of the secondconductivity type constitutes a drain region 63. The dopantconcentration in the drain regions 63 may be in a range from5.0×10¹⁹/cm³ to 2.0×10²¹/cm³, although lesser and greater dopantconcentrations may also be used. The doped semiconductor material maybe, for example, doped poly silicon.

Each remaining portion of the semiconductor channel material layer 60Lconstitutes a vertical semiconductor channel 60 through which electricalcurrent may flow when a vertical NAND device including the verticalsemiconductor channel 60 is turned on. A tunneling dielectric layer 56is surrounded by a charge storage layer 54, and laterally surrounds avertical semiconductor channel 60. Each adjoining set of a blockingdielectric layer 52, a charge storage layer 54, and a tunnelingdielectric layer 56 collectively constitute a memory film 50, which maystore electrical charges with a macroscopic retention time. In someembodiments, a blocking dielectric layer 52 may not be present in thememory film 50 at this step, and a blocking dielectric layer may besubsequently formed after formation of backside recesses. As usedherein, a macroscopic retention time refers to a retention time suitablefor operation of a memory device as a permanent memory device such as aretention time in excess of 24 hours.

Each combination of a memory film 50 and a vertical semiconductorchannel 60 (which is a vertical semiconductor channel) within a memoryopening 49 constitutes a memory stack structure 55. The memory stackstructure 55 is a combination of a vertical semiconductor channel 60, atunneling dielectric layer 56, a plurality of memory elements comprisingportions of the charge storage layer 54, and an optional blockingdielectric layer 52. Each combination of a memory stack structure 55, adielectric core 62, and a drain region 63 within a memory opening 49constitutes a memory pillar structure 58. The in-process source-levelmaterial layers 110′, the first-tier structure (132, 142, 170, 165), thesecond-tier structure (232, 242, 270, 265, 72), the inter-tierdielectric layer 180, and the memory pillar structures 58 collectivelyconstitute a memory-level assembly.

Referring to FIG. 12 , the exemplary structure is illustrated afterformation of the memory pillar structures 58. Support pillar structures20 are formed in the support openings 19 concurrently with formation ofthe memory pillar structures 58. Each support pillar structure 20 mayhave a same set of components as a memory pillar structure 58.

Formation of memory pillar structures 58 and the support pillarstructures 20 through the alternating stacks {(132, 142), (232, 242)}can result in generation of mechanical stress across the semiconductordie 900 because the memory pillar structures 58 and the support pillarstructures 20 are formed primarily within the memory array regions 100and the contact regions 200. According to an aspect of the presentdisclosure, deformation within the alternating stacks {(132, 142), (232,242)} can be measured by measuring lateral distances between pairs ofbump stack structures BSS. Further, in case the protrusion structures270P2 are formed over the alternating stacks {(132, 142), (232, 242)}are formed in areas that are laterally spaced from the bump stackstructures BSS, deformation within the alternating stacks {(132, 142),(232, 242)} can be determined (i.e., calculated) by measuring lateraldistances between pairs of a respective one of bump stack structures BSSand a respective one of the protrusion structures 270P2 and/or bymeasuring lateral distances between pairs of protrusion structures270P2.

Referring to FIGS. 13A and 13B, a first contact-level dielectric layer280 may be formed over the second-tier structure (232, 242, 270, 265,72). The first contact-level dielectric layer 280 includes a dielectricmaterial such as silicon oxide, and may be formed by a conformal ornon-conformal deposition process. For example, the first contact-leveldielectric layer 280 may include undoped silicate glass and may have athickness in a range from 100 nm to 600 nm, although lesser and greaterthicknesses may also be used.

A photoresist layer may be applied over the first contact-leveldielectric layer 280 and may be lithographically patterned to formelongated openings that extend along the first horizontal direction hd1between clusters of memory pillar structures 58. Backside trenches 79may be formed by transferring the pattern in the photoresist layer (notshown) through the first contact-level dielectric layer 280, thesecond-tier structure (232, 242, 270, 265, 72), and the first-tierstructure (132, 142, 170, 165), and into the in-process source-levelmaterial layers 110′. Portions of the first contact-level dielectriclayer 280, the second-tier structure (232, 242, 270, 265, 72), thefirst-tier structure (132, 142, 170, 165), and the in-processsource-level material layers 110′ that underlie the openings in thephotoresist layer may be removed to form the backside trenches 79. Inone embodiment, the backside trenches 79 may be formed between clustersof memory stack structures 55. The clusters of the memory stackstructures 55 may be laterally spaced apart along the second horizontaldirection hd2 by the backside trenches 79.

Referring to FIGS. 14 and 15A, a backside trench spacer 77 may be formedon sidewalls of each backside trench 79. For example, a conformal spacermaterial layer may be deposited in the backside trenches 79 and over thefirst contact-level dielectric layer 280, and may be anisotropicallyetched to form the backside trench spacers 77. The backside trenchspacers 77 include a material that is different from the material of thesource-level sacrificial layer 104. For example, the backside trenchspacers 77 may include silicon nitride.

Referring to FIG. 15B, an etchant that etches the material of thesource-level sacrificial layer 104 selective to the materials of thefirst-tier alternating stack (132, 142), the second alternating stack(232, 242), the first and second insulating cap layers (170, 270), thefirst contact-level dielectric layer 280, the upper sacrificial liner105, and the lower sacrificial liner 103 may be introduced into thebackside trenches in an isotropic etch process. For example, if thesource-level sacrificial layer 104 includes undoped amorphous silicon oran undoped amorphous silicon-germanium alloy, the backside trenchspacers 77 include silicon nitride, and the upper and lower sacrificialliners (105, 103) include silicon oxide, a wet etch process using hottrimethyl-2 hydroxyethyl ammonium hydroxide (“hot TMY”) or tetramethylammonium hydroxide (TMAH) may be used to remove the source-levelsacrificial layer 104 selective to the backside trench spacers 77 andthe upper and lower sacrificial liners (105, 103). A source cavity 109is formed in the volume from which the source-level sacrificial layer104 is removed.

Wet etch chemicals such as hot TMY and TMAH are selective to dopedsemiconductor materials such as the p-doped semiconductor materialand/or the n-doped semiconductor material of the upper source-levelsemiconductor layer 116 and the lower source-level semiconductor layer112. Thus, use of selective wet etch chemicals such as hot TMY and TMAHfor the wet etch process that forms the source cavity 109 provides alarge process window against etch depth variation during formation ofthe backside trenches 79. Specifically, even if sidewalls of the uppersource-level semiconductor layer 116 are physically exposed or even if asurface of the lower source-level semiconductor layer 112 is physicallyexposed upon formation of the source cavity 109 and/or the backsidetrench spacers 77, collateral etching of the upper source-levelsemiconductor layer 116 and/or the lower source-level semiconductorlayer 112 is minimal, and the structural change to the exemplarystructure caused by accidental physical exposure of the surfaces of theupper source-level semiconductor layer 116 and/or the lower source-levelsemiconductor layer 112 during manufacturing steps do not result indevice failures. Each of the memory pillar structures 58 is physicallyexposed to the source cavity 109. Specifically, each of the memorypillar structures 58 includes a sidewall and that are physically exposedto the source cavity 109.

Referring to FIG. 15C, a sequence of isotropic etchants, such as wetetchants, may be applied to the physically exposed portions of thememory films 50 to sequentially etch the various component layers of thememory films 50 from outside to inside, and to physically exposecylindrical surfaces of the vertical semiconductor channels 60 at thelevel of the source cavity 109. The upper and lower sacrificial liners(105, 103) may be collaterally etched during removal of the portions ofthe memory films 50 located at the level of the source cavity 109. Thesource cavity 109 may be expanded in volume by removal of the portionsof the memory films 50 at the level of the source cavity 109 and theupper and lower sacrificial liners (105, 103). A top surface of thelower source-level semiconductor layer 112 and a bottom surface of theupper source-level semiconductor layer 116 may be physically exposed tothe source cavity 109. The source cavity 109 is formed by isotropicallyetching the source-level sacrificial layer 104 and a bottom portion ofeach of the memory films 50 selective to at least one source-levelsemiconductor layer (such as the lower source-level semiconductor layer112 and the upper source-level semiconductor layer 116) and the verticalsemiconductor channels 60.

Referring to FIG. 15D, a semiconductor material having a doping of thesecond conductivity type may be deposited on the physically exposedsemiconductor surfaces around the source cavity 109. The physicallyexposed semiconductor surfaces include bottom portions of outersidewalls of the vertical semiconductor channels 60 and a horizontalsurface of the at least one source-level semiconductor layer (such as abottom surface of the upper source-level semiconductor layer 116 and/ora top surface of the lower source-level semiconductor layer 112). Forexample, the physically exposed semiconductor surfaces may include thebottom portions of outer sidewalls of the vertical semiconductorchannels 60, the top horizontal surface of the lower source-levelsemiconductor layer 112, and the bottom surface of the uppersource-level semiconductor layer 116.

In one embodiment, the doped semiconductor material of the secondconductivity type may be deposited on the physically exposedsemiconductor surfaces around the source cavity 109 by a selectivesemiconductor deposition process. A semiconductor precursor gas, anetchant, and a dopant gas may be flowed concurrently into a processchamber including the exemplary structure during the selectivesemiconductor deposition process. For example, the semiconductorprecursor gas may include silane, disilane, or dichlorosilane, theetchant gas may include gaseous hydrogen chloride, and the dopant gasmay include a hydride of a dopant atom such as phosphine, arsine,stibine, or diborane. In this case, the selective semiconductordeposition process grows a doped semiconductor material having a dopingof the second conductivity type from physically exposed semiconductorsurfaces around the source cavity 109. The deposited doped semiconductormaterial forms a source contact layer 114, which may contact sidewallsof the vertical semiconductor channels 60. The atomic concentration ofthe dopants of the second conductivity type in the depositedsemiconductor material may be in a range from 1.0×10¹⁹/cm³ to2.0×10²¹/cm³, such as from 2.0×10²⁰/cm³ to 8.0×10²⁰/cm³. The sourcecontact layer 114 as initially formed may consist essentially ofsemiconductor atoms and dopant atoms of the second conductivity type.Alternatively, at least one non-selective doped semiconductor materialdeposition process may be used to form the source contact layer 114.Optionally, one or more etch back processes may be used in combinationwith a plurality of selective or non-selective deposition processes toprovide a seamless and/or voidless source contact layer 114.

The duration of the selective semiconductor deposition process may beselected such that the source cavity 109 is filled with the sourcecontact layer 114, and the source contact layer 114 contacts bottom endportions of inner sidewalls of the backside trench spacers 77. In oneembodiment, the source contact layer 114 may be formed by selectivelydepositing a doped semiconductor material having a doping of the secondconductivity type from semiconductor surfaces around the source cavity109. In one embodiment, the doped semiconductor material may includedoped polysilicon. Thus, the source-level sacrificial layer 104 may bereplaced with the source contact layer 114.

The layer stack including the lower source-level semiconductor layer112, the source contact layer 114, and the upper source-levelsemiconductor layer 116 constitutes a buried source layer (112, 114,116). The set of layers including the buried source layer (112, 114,116), the source-level insulating layer 117, and the source-select-levelsemiconductor layer 118 constitutes source-level material layers 110,which replaces the in-process source-level material layers 110′.

Referring to FIGS. 15E and 16 , the backside trench spacers 77 may beremoved selective to the insulating layers (132, 232), the first andsecond insulating cap layers (170, 270), the first contact-leveldielectric layer 280, and the source contact layer 114 using anisotropic etch process. For example, if the backside trench spacers 77include silicon nitride, a wet etch process using hot phosphoric acidmay be performed to remove the backside trench spacers 77. In oneembodiment, the isotropic etch process that removes the backside trenchspacers 77 may be combined with a subsequent isotropic etch process thatetches the sacrificial material layers (142, 242) selective to theinsulating layers (132, 232), the first and second insulating cap layers(170, 270), the first contact-level dielectric layer 280, and the sourcecontact layer 114.

An oxidation process may be performed to convert physically exposedsurface portions of semiconductor materials into dielectricsemiconductor oxide portions. For example, surfaces portions of thesource contact layer 114 and the upper source-level semiconductor layer116 may be converted into dielectric semiconductor oxide plates 122, andsurface portions of the source-select-level semiconductor layer 118 maybe converted into annular dielectric semiconductor oxide spacers 124.

Referring to FIG. 17 , the sacrificial material layers (142, 242) areremoved selective to the insulating layers (132, 232), the first andsecond insulating cap layers (170, 270), the first contact-leveldielectric layer 280, and the source contact layer 114, the dielectricsemiconductor oxide plates 122, and the annular dielectric semiconductoroxide spacers 124. For example, an etchant that selectively etches thematerials of the sacrificial material layers (142, 242) with respect tothe materials of the insulating layers (132, 232), the first and secondinsulating cap layers (170, 270), the retro-stepped dielectric materialportions (165, 265), and the material of the outermost layer of thememory films 50 may be introduced into the backside trenches 79, forexample, using an isotropic etch process. For example, the sacrificialmaterial layers (142, 242) may include silicon nitride, the materials ofthe insulating layers (132, 232), the first and second insulating caplayers (170, 270), the retro-stepped dielectric material portions (165,265), and the outermost layer of the memory films 50 may include siliconoxide materials.

The isotropic etch process may be a wet etch process using a wet etchsolution, or may be a gas phase (dry) etch process in which the etchantis introduced in a vapor phase into the backside trench 79. For example,if the sacrificial material layers (142, 242) include silicon nitride,the etch process may be a wet etch process in which the exemplarystructure is immersed within a wet etch tank including phosphoric acid,which etches silicon nitride selective to silicon oxide, silicon, andvarious other materials used in the art.

Backside recesses (143, 243) are formed in volumes from which thesacrificial material layers (142, 242) are removed. The backsiderecesses (143, 243) include first backside recesses 143 that are formedin volumes from which the first sacrificial material layers 142 areremoved and second backside recesses 243 that are formed in volumes fromwhich the second sacrificial material layers 242 are removed. Each ofthe backside recesses (143, 243) may be a laterally extending cavityhaving a lateral dimension that is greater than the vertical extent ofthe cavity. In other words, the lateral dimension of each of thebackside recesses (143, 243) may be greater than the height of therespective backside recess (143, 243). A plurality of backside recesses(143, 243) may be formed in the volumes from which the material of thesacrificial material layers (142, 242) is removed. Each of the backsiderecesses (143, 243) may extend substantially parallel to the top surfaceof the substrate semiconductor layer 9. A backside recess (143, 243) maybe vertically bounded by a top surface of an underlying insulating layer(132, 232) and a bottom surface of an overlying insulating layer (132,232). In one embodiment, each of the backside recesses (143, 243) mayhave a uniform height throughout.

Referring to FIGS. 18A-18E, a backside blocking dielectric layer (notshown) may be optionally deposited in the backside recesses (143, 243)and the backside trenches 79 and over the first contact-level dielectriclayer 280. The backside blocking dielectric layer includes a dielectricmaterial such as a dielectric metal oxide, silicon oxide, or acombination thereof. For example, the backside blocking dielectric layermay include aluminum oxide. The backside blocking dielectric layer maybe formed by a conformal deposition process such as atomic layerdeposition or chemical vapor deposition. The thickness of the backsideblocking dielectric layer may be in a range from 1 nm to 20 nm, such asfrom 2 nm to 10 nm, although lesser and greater thicknesses may also beused.

At least one conductive material may be deposited in the plurality ofbackside recesses (143, 243), on the sidewalls of the backside trenches79, and over the first contact-level dielectric layer 280. The at leastone conductive material may be deposited by a conformal depositionmethod, which may be, for example, chemical vapor deposition (CVD),atomic layer deposition (ALD), electroless plating, electroplating, or acombination thereof. The at least one conductive material may include anelemental metal, an intermetallic alloy of at least two elementalmetals, a conductive nitride of at least one elemental metal, aconductive metal oxide, a conductive doped semiconductor material, aconductive metal-semiconductor alloy such as a metal silicide, alloysthereof, and combinations or stacks thereof.

In one embodiment, the at least one conductive material may include atleast one metallic material, i.e., an electrically conductive materialthat includes at least one metallic element. Non-limiting exemplarymetallic materials that may be deposited in the backside recesses (143,243) include tungsten, tungsten nitride, titanium, titanium nitride,tantalum, tantalum nitride, cobalt, and ruthenium. For example, the atleast one conductive material may include a conductive metallic nitrideliner that includes a conductive metallic nitride material such as TiN,TaN, WN, or a combination thereof, and a conductive fill material suchas W, Co, Ru, Mo, Cu, or combinations thereof. In one embodiment, the atleast one conductive material for filling the backside recesses (143,243) may be a combination of titanium nitride layer and a tungsten fillmaterial.

Electrically conductive layers (146, 246) may be formed in the backsiderecesses (143, 243) by deposition of the at least one conductivematerial. A plurality of first electrically conductive layers 146 may beformed in the plurality of first backside recesses 143, a plurality ofsecond electrically conductive layers 246 may be formed in the pluralityof second backside recesses 243, and a continuous metallic materiallayer (not shown) may be formed on the sidewalls of each backside trench79 and over the first contact-level dielectric layer 280. Each of thefirst electrically conductive layers 146 and the second electricallyconductive layers 246 may include a respective conductive metallicnitride liner and a respective conductive fill material. Thus, the firstand second sacrificial material layers (142, 242) may be replaced withthe first and second electrically conductive layers (146, 246),respectively. Specifically, each first sacrificial material layer 142may be replaced with an optional portion of the backside blockingdielectric layer and a first electrically conductive layer 146, and eachsecond sacrificial material layer 242 may be replaced with an optionalportion of the backside blocking dielectric layer and a secondelectrically conductive layer 246. A backside cavity is present in theportion of each backside trench 79 that is not filled with thecontinuous metallic material layer.

Residual conductive material may be removed from inside the backsidetrenches 79. Specifically, the deposited metallic material of thecontinuous metallic material layer may be etched back from the sidewallsof each backside trench 79 and from above the first contact-leveldielectric layer 280, for example, by an anisotropic or isotropic etch.Each remaining portion of the deposited metallic material in the firstbackside recesses constitutes a first electrically conductive layer 146.Each remaining portion of the deposited metallic material in the secondbackside recesses constitutes a second electrically conductive layer246. Sidewalls of the first electrically conductive material layers 146and the second electrically conductive layers may be physically exposedto a respective backside trench 79. The backside trenches may have apair of curved sidewalls having a non-periodic width variation along thefirst horizontal direction hd1 and a non-linear width variation alongthe vertical direction.

Each electrically conductive layer (146, 246) may be a conductive sheetincluding openings therein. A first subset of the openings through eachelectrically conductive layer (146, 246) may be filled with memorypillar structures 58. A second subset of the openings through eachelectrically conductive layer (146, 246) may be filled with the supportpillar structures 20. Each electrically conductive layer (146, 246) mayhave a lesser area than any underlying electrically conductive layer(146, 246) because of the first and second stepped surfaces. Eachelectrically conductive layer (146, 246) may have a greater area thanany overlying electrically conductive layer (146, 246) because of thefirst and second stepped surfaces.

In some embodiment, drain-select-level isolation structures 72 may beprovided at topmost levels of the second electrically conductive layers246. A subset of the second electrically conductive layers 246 locatedat the levels of the drain-select-level isolation structures 72constitutes drain select gate electrodes. A subset of the electricallyconductive layer (146, 246) located underneath the drain select gateelectrodes may function as combinations of a control gate and a wordline located at the same level. The control gate electrodes within eachelectrically conductive layer (146, 246) are the control gate electrodesfor a vertical memory device including the memory stack structure 55.

Each of the memory stack structures 55 comprises a vertical stack ofmemory elements located at each level of the electrically conductivelayers (146, 246). A subset of the electrically conductive layers (146,246) may comprise word lines for the memory elements. The semiconductordevices in the underlying peripheral device region 700 may comprise wordline switch devices configured to control a bias voltage to respectiveword lines. The memory-level assembly is located over the substratesemiconductor layer 9. The memory-level assembly includes at least onealternating stack (132, 146, 232, 246) and memory stack structures 55vertically extending through the at least one alternating stack (132,146, 232, 246).

Referring to FIGS. 19A-19C, a dielectric material layer may beconformally deposited in the backside trenches 79 and over the firstcontact-level dielectric layer 280 by a conformal deposition process.The dielectric material layer may include, for example, silicon oxide.

Referring to FIGS. 20A and 20B, a second contact-level dielectric layer282 may be formed over the first contact-level dielectric layer 280. Thesecond contact-level dielectric layer 282 includes a dielectric materialsuch as silicon oxide, and may have a thickness in a range from 100 nmto 600 nm, although lesser and greater thicknesses may also be used.

A photoresist layer (not shown) may be applied over the secondcontact-level dielectric layer 282, and may be lithographicallypatterned to form various contact via openings. For example, openingsfor forming drain contact via structures may be formed in the memoryarray region 100, and openings for forming staircase region contact viastructures may be formed in the staircase region 200. An anisotropicetch process is performed to transfer the pattern in the photoresistlayer through the second and first contact-level dielectric layers (282,280) and underlying dielectric material portions. The drain regions 63and the electrically conductive layers (146, 246) may be used as etchstop structures. Drain contact via cavities may be formed over eachdrain region 63, and staircase-region contact via cavities may be formedover each electrically conductive layer (146. 246) at the steppedsurfaces underlying the first and second retro-stepped dielectricmaterial portions (165, 265). The photoresist layer may be subsequentlyremoved, for example, by ashing.

Drain contact via structures 88 are formed in the drain contact viacavities and on a top surface of a respective one of the drain regions63. Staircase-region contact via structures 86 are formed in thestaircase-region contact via cavities and on a top surface of arespective one of the electrically conductive layers (146, 246). Thestaircase-region contact via structures 86 may include drain selectlevel contact via structures that contact a subset of the secondelectrically conductive layers 246 that function as drain select levelgate electrodes. Further, the staircase-region contact via structures 86may include word line contact via structures that contact electricallyconductive layers (146, 246) that underlie the drain select level gateelectrodes and function as word lines for the memory stack structures55.

Referring to FIG. 21 , peripheral-region via cavities may be formedthrough the second and first contact-level dielectric layers (282, 280),the second and first retro-stepped dielectric material portions (265,165), and the drain-side dielectric layers 768 to top surfaces of afirst subset of the lower-level metal interconnect structure 780 in theperipheral device region 400. At least one conductive material may bedeposited in the peripheral-region via cavities. Excess portions of theat least one conductive material may be removed from above thehorizontal plane including the top surface of the second contact-leveldielectric layer 282. Each remaining portion of the at least oneconductive material in a peripheral-region via cavity constitutes aperipheral-region contact via structure 488.

At least one additional dielectric layer may be formed over thecontact-level dielectric layers (280, 282), and additional metalinterconnect structures (herein referred to as upper-level metalinterconnect structures) may be formed in the at least one additionaldielectric layer. For example, the at least one additional dielectriclayer may include a line-level dielectric layer 290 that is formed overthe contact-level dielectric layers (280, 282). The upper-level metalinterconnect structures may include bit lines 98 contacting a respectiveone of the drain contact via structures 88, and interconnection linestructures 96 contacting, and/or electrically connected to, at least oneof the staircase-region contact via structures 86 and/or theperipheral-region contact via structures 488. The word line contact viastructures (which are provided as a subset of the staircase-regioncontact via structures 86) may be electrically connected to the wordline driver circuit through a subset of the lower-level metalinterconnect structures 780 and through a subset of theperipheral-region contact via structures 488.

In one embodiment, the three-dimensional memory device comprises amonolithic three-dimensional NAND memory device, the electricallyconductive strips (146, 246) comprise, or are electrically connected to,a respective word line of the monolithic three-dimensional NAND memorydevice, the substrate 8 comprises a silicon substrate, the monolithicthree-dimensional NAND memory device comprises an array of monolithicthree-dimensional NAND strings over the silicon substrate, and at leastone memory cell in a first device level of the array of monolithicthree-dimensional NAND strings is located over another memory cell in asecond device level of the array of monolithic three-dimensional NANDstrings. The silicon substrate may contain an integrated circuitcomprising a driver circuit for the memory device located thereon, theelectrically conductive strips (146, 246) comprise a plurality ofcontrol gate electrodes having a strip shape extending substantiallyparallel to the top surface of the substrate 8, the plurality of controlgate electrodes comprise at least a first control gate electrode locatedin the first device level and a second control gate electrode located inthe second device level. The array of monolithic three-dimensional NANDstrings comprises a plurality of semiconductor channels 60, wherein atleast one end portion of each of the plurality of semiconductor channels60 extends substantially perpendicular to a top surface of the substrate8, and one of the plurality of semiconductor channels including thevertical semiconductor channel 60. The array of monolithicthree-dimensional NAND strings comprises a plurality of charge storageelements (comprising portions of the memory films 50), each chargestorage element located adjacent to a respective one of the plurality ofsemiconductor channels 60.

Referring to all drawings and according to various embodiments of thepresent disclosure, a three-dimensional memory device includes analternating stack of insulating layers (132, 232) and electricallyconductive layers (146, 246), pillar structures 50 vertically extendingthrough the alternating stack {(132, 232), (146, 246)} and comprising avertical semiconductor channel 60 and a memory film 50, bump stackstructures BSS including a base bump portion 118P located underneath thealternating stack and a respective subset of the bump portions BPlocated in the alternating stack that overlie the base bump portion188P, and protrusion structures PS located over the alternating stackand laterally spaced from the bump stack structures BSS. Each of theinsulating layers and the electrically conductive layers include aplanar portion PP located between a planar top surface and a planarbottom surface and the bump portions BP that are adjoined to the planarportion PP at a respective periphery P and having a respective raisedtop surface that is vertically raised from the planar top surface and arespective raised bottom surface that is raised from the planar bottomsurface.

In one embodiment, the bump portions BP and the planar portion PP have asame thickness for each layer of the insulating layers (132, 232) andthe electrically conductive layers (146, 246). In one embodiment, avolume ratio of the planar portion PP to the bump portion BP in each ofthe insulating layers (132, 232) and the electrically conductive layers(146, 246) is greater than 0.8 and less than 1.

In one embodiment, each bump portion BP comprises: a respective bottomedge at which the planar bottom surface of the layer adjoins a firsttapered or vertical surface of the layer; and a respective top edge atwhich the planar top surface of the layer adjoins a second tapered orvertical surface of the layer. In one embodiment, the respective topedge is laterally offset outward from the respective bottom edge by auniform lateral offset distance in a plan view, i.e., a view along avertical direction. In one embodiment, the uniform lateral offsetdistance is in a range from 80% to 100% of a thickness of the insulatinglayers (132, 142) and the electrically conductive layers (146, 246). Inone embodiment, within each of the bump stack structures BSS, eachoverlying periphery P within the respective subset of bump portions islaterally offset outward from any underlying periphery P within therespective subset of the bump portions.

In one embodiment, a subset of the pillar structures (58, 20) verticallyextends through the bump stack structures BSS. In one embodiment, thesubset of the pillar structures (58, 20) comprises a pillar structure(58 or 20) that extends through planar portions of a first subset oflayers within the alternating stack (for example, a bottommost firstinsulating layer 132) and through bump portions of a second subset ofthe layers within the alternating stack that overlies the first subset(for example, a topmost second insulating layer 232).

In one embodiment, the bump stack structures BSS vertically extends froma bottommost layer within the alternating stack to a topmost layerwithin the alternating stack. In one embodiment, the verticalsemiconductor channels 60 have a doping of a first conductivity type;and each of the pillar structures (58, 20) comprises a drain region 63having a doping of a second conductive type and contacting an upper endof a respective one of the vertical semiconductor channels 60.

In one embodiment, the three-dimensional memory device comprises: astaircase region in which each electrically conductive layer (146, 246)other than a bottommost electrically conductive layer within thealternating stack {(132, 146), (232, 246)} has a lesser lateral extentthan any underlying electrically conductive layer (146, 246); andstaircase-region contact via structures 86 contacting a top surface of arespective one of the electrically conductive layers (146, 246) andlocated in the staircase region.

Although the foregoing refers to particular embodiments, it will beunderstood that the disclosure is not so limited. It will occur to thoseof ordinary skill in the art that various modifications may be made tothe disclosed embodiments and that such modifications are intended to bewithin the scope of the disclosure. Compatibility is presumed among allembodiments that are not alternatives of one another. The word“comprise” or “include” contemplates all embodiments in which the word“consist essentially of” or the word “consists of” replaces the word“comprise” or “include,” unless explicitly stated otherwise. Where anembodiment using a particular structure and/or configuration isillustrated in the present disclosure, it is understood that the presentdisclosure may be practiced with any other compatible structures and/orconfigurations that are functionally equivalent provided that suchsubstitutions are not explicitly forbidden or otherwise known to beimpossible to one of ordinary skill in the art. All of the publications,patent applications and patents cited herein are incorporated herein byreference in their entirety.

What is claimed is:
 1. A three-dimensional memory device, comprising: analternating stack of insulating layers and electrically conductivelayers; pillar structures vertically extending through the alternatingstack, wherein each of the pillar structures comprises a verticalsemiconductor channel and a memory film; bump stack structurescomprising a base bump portion located underneath the alternating stackand a respective subset of the bump portions located in the alternatingstack that overlie the base bump portion; and protrusion structureslocated over the alternating stack and laterally spaced from the bumpstack structures, wherein each of the insulating layers and theelectrically conductive layers comprise a planar portion located betweena planar top surface and a planar bottom surface and the bump portionsthat are adjoined to the planar portion at a respective periphery andhaving a respective raised top surface that is vertically raised fromthe planar top surface and a respective raised bottom surface that israised from the planar bottom surface.
 2. The three-dimensional memorydevice of claim 1, wherein the bump portions and the planar portion havea same thickness for each layer of the insulating layers and theelectrically conductive layers.
 3. The three-dimensional memory deviceof claim 2, wherein a volume ratio of the planar portion to the bumpportion in each of the insulating layers and the electrically conductivelayers is greater than 0.8 and less than
 1. 4. The three-dimensionalmemory device of claim 2, wherein each bump portion comprises: arespective bottom edge at which the planar bottom surface of the layeradjoins a first tapered or vertical surface of the layer; and arespective top edge at which the planar top surface of the layer adjoinsa second tapered or vertical surface of the layer.
 5. Thethree-dimensional memory device of claim 4, wherein the respective topedge is laterally offset outward from the respective bottom edge by auniform lateral offset distance in a plan view.
 6. The three-dimensionalmemory device of claim 5, wherein the uniform lateral offset distance isin a range from 80% to 100% of a thickness of the insulating layers andthe electrically conductive layers.
 7. The three-dimensional memorydevice of claim 1, wherein within each of the bump stack structures,each overlying periphery within the respective subset of bump portionsis laterally offset outward from any underlying periphery within therespective subset of the bump portions.
 8. The three-dimensional memorydevice of claim 1, wherein a subset of the pillar structures verticallyextends through the bump stack structures.
 9. The three-dimensionalmemory device of claim 8, wherein the subset of the pillar structurescomprises a pillar structure that extends through planar portions of afirst subset of layers within the alternating stack and through bumpportions of a second subset of the layers within the alternating stackthat overlies the first subset.
 10. The three-dimensional memory deviceof claim 1, wherein the bump stack structures vertically extend from abottommost layer within the alternating stack to a topmost layer withinthe alternating stack.
 11. The three-dimensional memory device of claim1, wherein: the vertical semiconductor channels have a doping of a firstconductivity type; and each of the pillar structures comprises a drainregion having a doping of a second conductive type and contacting anupper end of a respective one of the vertical semiconductor channels.12. The three-dimensional memory device of claim 1, further comprising:a staircase region in which each electrically conductive layer otherthan a bottommost electrically conductive layer within the alternatingstack has a lesser lateral extent than any underlying electricallyconductive layer; and staircase-region contact via structures contactinga top surface of a respective one of the electrically conductive layersand located in the staircase region.
 13. A method of forming asemiconductor structure, comprising: forming base bump portions over asubstrate; forming an alternating stack of insulating layers and spacermaterial layers, wherein the spacer material layers are formed as, orare subsequently replaced with, electrically conductive layers, whereineach layer within the alternating stack comprises a planar portionvertically extending between a planar top surface and a planar bottomsurface and bump portions that overlie a respective one of the base bumpportions to form bump stack structures comprising a respective one ofthe base bump portions and a respective subset of the bump portions ofthe alternating stack are formed; forming protrusion structures locatedover the alternating stack and laterally spaced from the bump stackstructures; and forming pillar structures through the alternating stack,wherein each of the pillar structures comprises a memory film and avertical semiconductor channel.
 14. The method of claim 13, furthercomprising determining deformation within the alternating stack bymeasuring lateral distances between the protrusion structures and thebump stack structures.
 15. The method of claim 14, wherein theprotrusion structures are formed by depositing and patterning aninsulating cap layer over the alternating stack.
 16. The method of claim15, wherein the protrusion structures comprise portions of theinsulating cap layer having a greater thickness than portions of theinsulating cap adjacent to the protrusion structures.
 17. The method ofclaim 15, wherein the base bump portions comprise portions of asemiconductor material layer having a greater thickness than portions ofthe semiconductor material layer adjacent to the base bump portions. 18.The method of claim 13, wherein each layer of the insulating layers andthe spacer material layers is deposited by a respective conformaldeposition process.
 19. The method of claim 18, further comprisingreplacing the spacer material layers with the electrically conductivelayers.
 20. The method of claim 13, further comprising: formingvertically extending openings through the alternating stack; depositinga memory material and a semiconductor channel material within each ofthe openings; and removing excess portions of the memory material andthe semiconductor channel material from above the alternating stack,wherein the pillar structures comprise remaining portions of the memorymaterial and the semiconductor channel material.